About the authors Dr G. Neil Martin is Reader in Psychology at Middlesex University, UK
fourth edition
Dr Neil R. Carlson is Professor of Psychology at the University of Massachusetts, USA
“The perfect balance between scientific rigour and comprehensiveness on the one hand, and fun stuff that will maintain students’ interest on the other. One of the best, if not the best, introductory textbooks available today.”
Dr William Buskist is Professor of Psychology at Auburn University, USA
“This new edition gives the reader a clear understanding of even the most difficult concepts in psychology. Features like ‘Controversies’ and ‘Cutting Edge’ help to locate psychology’s place in the world. An essential read for undergraduates.”
fourth edition
fourth edition
Dr Phil Higham, University of Southampton
G. Neil Martin Neil R. Carlson William Buskist
Dr Kevin Silber, University of Derby
“Achieves a high academic standard and at the same time is written in an accessible manner.” Dr Edward Edgerton, University of the West of Scotland “This accessible, authoritative text will be of use to all scholars, whether starting out or with considerable experience. It balances depth with breadth and its refreshing style will appeal to all types of learner.” Dr Kate Eames, Coventry University
The fourth edition of psychology introduces students to the field with its accessible, lively and comprehensive coverage. Fully revised and updated throughout, this book offers a rigorous and critical coverage. Key features:
•
‘Conceptual and historical issues in psychology’ are highlighted to encourage students to consider different perspectives and debates
•
‘Cutting Edge’ introduces novel and important research in the field
•
‘Psychology in Action’ highlights how psychological ideas and principles apply to the real world
•
‘Controversies in Psychological science’ explores debates and issues within the field
•
‘International perspectives’ provides a cross-cultural review of a topic.
Richly supported by examples, illustrations and photos drawn from Europe and across the world, this stimulating text will engage the student and provide an invaluable aid to learning.
Psychology 4/e comes with MyPsychLab, an interactive online study resource. Take a test to get a personal study plan and explore video and audio activities, animations, research updates, and additional question material. Use the access code included at the back of the book and go to www.MyPsychLab.co.uk to register.
Martin Carlson Buskist
Cover photograph: Christopher Pillitz/ Getty Images
ACCESS CODE INSIDE unlock valuable online learning resources
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Psychology
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We work with leading authors to develop the strongest educational materials in psychology, bringing cutting-edge thinking and best learning practice to a global market. Under a range of well-known imprints, including Allyn and Bacon, we craft high quality print and electronic publications which help readers to understand and apply their content, whether studying or at work. To find out more about the complete range of our publishing, please visit us on the World Wide Web at: www.pearsoned.co.uk
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Psychology Fourth Edition G. Neil Martin Middlesex University, UK
Neil R. Carlson University of Massachusetts, USA
William Buskist Auburn University, USA
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PEARSON EDUCATION LIMITED Edinburgh Gate Harlow Essex CM20 2JE England and Associated Companies throughout the world Visit us on the World Wide Web at: www.pearsoned.co.uk Original edition published by Allyn and Bacon, A Pearson Education Company Needham Heights, Massachusetts, USA Copyright © 1997 by Allyn and Bacon First published by Pearson Education Limited in Great Britain in 2000 Second edition published in 2004 Third edition published in 2007 Fourth edition published in 2010 © Pearson Education Limited 2000, 2004, 2007, 2010 The rights of G. Neil Martin, Neil R. Carlson and William Buskist to be identified as authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, 6–10 Kirby Street, London EC1N 8TS. ISBN: 978-0-273-72011-9 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress 10 9 8 7 6 5 4 3 2 1 14 13 12 11 10 Typeset in 9.75/12pt Sabon by 30 Printed and bound by Rotolito Lombarda, Italy The publisher's policy is to use paper manufactured from sustainable forests.
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Brief contents
Preface to the fourth edition
xvii
Guided tour
xx
The authors
xxvi
Acknowledgements
1. The science of psychology
xxviii 2
2. Research methods in psychology
47
3. Evolution, genetics and behaviour
75
4. Psychology and neuroscience
113
5. Sensation
167
6. Perception
213
7. Learning and behaviour
257
8. Memory
291
9. Consciousness
337
10. Language
375
11. Intelligence and thinking
431
12. Developmental psychology
493
13. Motivation and emotion
553
14. Personality
609
15. Social cognition and attiudes
647
16. Interpersonal and group processes
679
17. Health psychology
727
18. Abnormal psychology
773
Appendix: Understanding research results
A1
Glossary
G1
References
R1
Indexes
I1
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Contents
Preface to the fourth edition Guided tour The authors Acknowledgements
xvii xx xxvi xxviii
1 The science of psychology What you should be able to do after reading Chapter 1 Questions to think about
3 3
What is psychology?
4
Psychology defined Cutting edge: How much of a science is psychology? Controversies in Psychological Science: Is psychology common sense? Explaining behaviour Established and emerging fields of psychology Psychology in action: How to detect a liar Cutting edge: I’m your biggest fan ... What makes a celebrity worshipper worship? Psychology in action: Psychology in the witness box Psychology – An international perspective
4 5 6 7 8 10 13 14 16
Psychology: a European perspective
18
Psychological training and status of psychology in Europe European views of psychology and psychologists
18 19
Psychology: the development of a science
20
Philosophical roots of psychology
20
Modern psychology: from the Leipzig laboratory to the cognitive revolution
24
Structuralism: Wilhelm Wundt Memory: Hermann Ebbinghaus Functionalism: William James and James Angell Evolution and heritability: Charles Darwin and Francis Galton Psychodynamic theory: Sigmund Freud Behaviourism: Edward Thorndike and Ivan Pavlov Behaviourism: John B. Watson Radical behaviourism: Edward Tolman and Clark Leonard Hull Radical behaviourism: Burrhus Frederic Skinner Genetic epistemology: Jean Piaget Gestalt psychology: Max Wertheimer Humanistic psychology The personality psychologists: Gordon Allport, Raymond Cattell, Hans Eysenck, Walter Mischel, Paul Costa and Robert McCrae The social psychologists
24 25 25 26 27 28 29 30 30 31 31 32
32 33
The cognitive revolution: beyond behaviourism The biological revolution Cognitive neuroscience: the future of the biology of the ‘mind’?
38
Conceptual and historical issues in psychological science
39
Chapter review Suggestions for further reading Journals to consult Website addresses Addresses: major international professional psychology organisations and societies
34 35
40 41 42 42 43
2 Research methods in psychology What you should be able to do after reading Chapter 2 Questions to think about
47 47
The process of discovery in psychology: the scientific method
48
Stages in experimentation Communicating the results of scientific research Cutting edge: Stories conquer statistics Controversies in Psychological Science: Psychology and the media Identifying the problem: getting an idea for research Quantitative research methods: designing an experiment Psychology in action: The Barnum effect Controversies in Psychological Science: How representative are samples in psychological research? Response bias – An international perspective Correlational studies Single-case studies Generalising from data Application of psychological research Qualitative analysis
48 48 49
59 60 63 64 64 65 65
Ethics
68
Research with human participants Informed consent Controversies in Psychological Science: Can research with animals help us to understand human behaviour? Chapter review Suggestions for further reading Journals to consult Website addresses
68 68
50 51 52 55
70 71 72 72 73
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Excitation and inhibition A simple neural circuit Neuromodulators: action at a distance
120 122 123
Techniques in psychobiology and neuroscience
124 124 126 126
92 93
Lesioning Studying brain injury: clinical neuropsychology Rehabilitation after brain damage Psychology in action: Using brain activity to overcome physical disability Psychophysiology: measuring CNS activity Psychophysiology: measuring activity outside the CNS Cutting edge: James Bond and the bloody consequences of Mortal Kombat Neuroimaging techniques Cutting edge: Love, friendship and neuroscience Cutting edge: The magic of neuroscience Caveats Controversies in Psychological Science: Can brain scanners detect deception? Modern brain stimulation: transcranial magnetic stimulation (TMS)
95
Control of behaviour
143
Organisation of the cerebral cortex Temporal sequencing of events Lateralisation of function Vision: the occipital lobe Audition: the temporal lobe Somatosensation and spatial perception: the parietal lobe Planning and moving: the frontal lobe
144 144 144 146 146 147 148
Control of internal functions and automatic behaviour
149
The brain stem The cerebellum Subcortical structures
149 149 150
Drugs and behaviour
154
3 Evolution, genetics and behaviour What you should be able to do after reading Chapter 3 Questions to think about
75 75
The development of evolutionary theory
76
In the beginning: the voyage of the Beagle The Origin of Species Natural selection and evolution Human evolution Natural selection and human evolution
77 77 78 81 82
Heredity and genetics
84
The basic principles of genetics Genetic diversity Influences of sex on heredity Mutations and chromosomal aberrations Epigentics Genetic disorders Psychology in action: The psychological consequences of genetic counselling Heredity and behaviour genetics Controversies in Psychological Science: Are attitudes genetically inherited?
85 87 87 89 90 90
Sociobiology
96
Reproductive strategies and the biological basis of parenting Physical attraction – An international perspective Cutting edge: Can I have your number? Cutting edge: Jealousy, infidelity and the brain Infidelity – An international perspective Altruism and kin selection Sociobiology and evolutionary psychology as an explanation for human behaviour? Chapter review Suggestions for further reading Journals to consult Website addresses
96 98 100 103 105 106 108 109 110 111 111
4 Psychobiology and neuroscience What you should be able to do after reading Chapter 4 Questions to think about
Psychobiology and neuroscience
113 113 114
The nervous system: the brain and its components
114
The central nervous system The peripheral nervous system Cells of the nervous system Neurotransmitters Myelination The action potential Synapses
114 115 117 117 118 118 119
Stimulating or inhibiting the release of transmitter substances Stimulating or blocking postsynaptic receptor molecules Inhibiting reuptake Sedatives Controversies in Psychological Science: What is drug addiction? Stimulants Drugs and altered states of consciousness Drug classification The psychology of cannabis use – An international perspective Chapter review Suggestions for further reading Journals to consult Website addresses
128 129 130 133 134 138 138 140 140 141
154 154 155 155 156 158 158 160 160 162 164 165 165
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CONTENTS
5 Sensation
6 Perception
What you should be able to do after reading Chapter 5 Questions to think about
167 167
What you should be able to do after reading Chapter 6 Questions to think about
213 213
Sensation and behaviour
168
The nature of perception
214
Sensory processing
168
Definition of perception
214
Transduction Sensory coding Psychophysics The principle of the just-noticeable difference
168 168 170 170
Perception of form
214
Vision
173
Light The eye and its functions Transduction of light by photoreceptors Adaptation to light and dark Eye movements Colour vision Defects in colour vision Psychology in action: Red light = danger? Synaesthesia
173 173 177 177 178 178 182 183 184
Figure and ground Organisation of elements: the principles of Gestalt Models of pattern perception Top-down processing: the role of context Direct perception: Gibson’s affordances Face perception
214 215 217 220 221 222
Perception of space and motion
227 227 231 232 233 233
Audition
185
Sound The ear and its functions Detecting and localising sounds in the environment The interaction between audition and vision Audition and the temporal cortex Cutting edge: Hearing voices Deafness
185 186 187 191 191 191 192
Depth perception Psychology in action: CCTV and face perception Distance and location Constancies of visual perception Visual perception across cultures Controversies in Psychological Science: How does language influence visual perception? Perception of motion Cutting edge: Content over style? Perception and the environment – An international perspective The psychology of art – An international perspective Brain mechanisms of visual perception The primary visual cortex How different are imagining and perceiving visual stimuli? The visual association cortex Brain damage and visual perception Perceptual disorders Psychology in action: How does brain injury affect artists? Chapter review Suggestions for further reading Journals to consult Website addresses
Gustation
193
Taste receptors and the sensory pathway The four or more qualities of taste The development of taste preference
193 195 196
Olfaction
197
Cutting edge: Cheese, body odour and the orbitofrontal cortex Odour perception – An international perspective Anatomy of the olfactory system Controversies in Psychological Science: Do human pheromones exist? The dimensions of odour Sex differences
198 198 199 200 202 203
The somatosenses
203
The skin senses The internal senses The vestibular senses Chapter review Suggestions for further reading Journals to consult Website addresses
204 206 206 207 208 209 210
235 237 237 239 240 241 241 242 243 244 246 250 252 253 254 255
7 Learning and behaviour What you should be able to do after reading Chapter 7 Questions to think about
257 257
The purpose of learning
258
Habituation
258
Classical conditioning
258
Pavlov’s serendipitous discovery The biological significance of classical conditioning Basic principles of classical conditioning Conditional emotional responses What is learned in classical conditioning? Neurobiological correlates of Pavlovian conditioning
259 260 260 261 263 263
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After behaviourism
263
Hull’s computational approach to learning Tolman and the cognitive map
264 265
Operant conditioning
266
The law of effect Skinner and operant behaviour The three-term contingency Reinforcement, punishment and extinction Other operant procedures and phenomena
266 267 267 268 270
Conditioning of complex behaviours
272
Aversive control of behaviour Psychology in action: Flavour aversions Applications of operant conditioning to human behaviour Controversies in Psychological Science: What is insight? Recent approaches to learning: computational modelling and neural networks
Learning in practice: being a student
281
Deep v. shallow learning Learning style Cutting edge: Personality and academic success Confidence The best way to understand a textbook Can the internet be used to teach successfully? Studying psychology – An international perspective Chapter review Suggestions for further reading Journals to consult Website addresses
281 282 282 283 283 284 285 286 287 287 288
Long-term memory: episodic and semantic memory
304
Autobiographical Memory – An international perspective Explicit and implicit memory
305 305
Remembering
306
273 275 275 276
Psychology in action: Using odours to retrieve memories Reconstruction: remembering as a creative process Psychology in action: How long does memory last? The malleability of memory Eyewitness testimony Eyewitness identification Cutting edge: Unbelievable accents Interference State-dependent memory: the effect of mood on recall Flashbulb memories
307 308 310 312 312 313 315 315 316 317
279
The biological basis of memory
319
Before memory: learning Where are long-term memories formed? Chemical modulation of long-term potentiation Amnesia Psychology in action: Memory at the movies ... The role of the hippocampus in memory Neuroimaging and memory Memory-enhancing drugs Controversies in Psychological Science: Do ‘smart drugs’ work? Chapter review Suggestions for further reading Journals to consult Website addresses
319 320 320 321 323 324 325 328
8 Memory What you should be able to do after reading Chapter 8 Questions to think about
291 291
Memory: an introduction
292
Types of memory
329 331 333 334 334
9 Consciousness What you should be able to do after reading Chapter 9 Questions to think about
337 337
292
Consciousness: an introduction
338
Sensory memory
292
Philosophical approaches to consciousness The meaning of ‘consciousness’
338 338
Iconic memory Echoic memory
293 293
Theories of consciousness
339
Short-term memory
293
Neurobiological theories Cognitive theories
339 342
Working memory Primacy and recency effects The limits of short-term and working memory Loss of information from short-term memory
294 297 298 299
Selective attention
342 343 344
Learning and encoding in long-term memory
300
The consolidation hypothesis Levels of processing Mnemonics Cutting edge: Something to chew over
300 300 301 304
Dichotic listening The cocktail-party phenomenon Controversies in Psychological Science: Does mobile phone use impair your driving? Background noise Noise – An international perspective Models of selective attention Visual information Inattentional blindness
345 347 348 348 349 350
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CONTENTS
Divided attention Brain mechanisms of selective attention Control of consciousness
350 351 352
Hypnosis
353
Psychology in action: Attention and pain The induction of hypnosis Characteristics of hypnosis Theories of hypnosis Controversies in Psychological Science: Can hypnosis reduce pain and stress?
353 354 354 355 356
Sleep
357
The stages of sleep Cutting edge: Evening types are more creative but are more maladaptive Functions of sleep Sleep deprivation Sleep-dependent memory consolidation Psychology in action: How sleep loss affects behaviour Dreaming Functions of dreams Role of REM sleep in brain development Brain mechanisms of sleep Sleep disorders Chapter review Suggestions for further reading Journals to consult Website addresses
357 360 360 360 361 362 364 364 366 366 367 369 371 371 372
10 Language What you should be able to do after reading Chapter 10 Questions to think about
375 375
The use of language
376
Psycholinguistics: the study of language acquisition and meaning Perception of speech Recognition of speech sounds Production of speech Recognition of words: the importance of context Understanding the meaning of speech The relationship between semantics and syntax Knowledge of the world What is meaning? Is there a universal language?
376 377 377 377 378 379 381 381 381 381
Reading
383
Psychology in action: Sex differences in communication Scanning text Phonetic and whole-word recognition The process of reading The dual-route model of reading Psychology in action: How children learn to read Understanding the meanings of words and sentences On the relative importance of consonants and vowels
383 384 385 386 387 389 391 391
Language acquisition by children
392
Perception of speech sounds by infants The pre-speech period and the first words – An international perspective Infant communication How adults talk to children Acquisition of adult rules of grammar Acquisition of meaning Bilingualism Is there a language acquisition device? Controversies in psychological science: Can other primates acquire language?
392
400
Brain development and language
403
The case of Genie Plasticity and language development Is half a brain enough?
403 403 404
The neuropsychology of language and language disorders
404
Language disorders Aphasia Psychology in action: The man who lost his language Specific language impairment Dyslexia
404 405 409 411 413
Word recognition and production: neuroimaging studies
418
Is there a visual word form area? Cutting edge: Irony – a look inside the brain Neuroimaging and language – An international perspective Braille and Sign language Neuropsychological models of language: a summary Caveats and complications Handedness Chapter review Suggestions for further reading Journals to consult Website addresses
419 419 420 421 422 423 424 425 427 428 428
393 394 394 395 396 398 398
11 Intelligence and thinking What you should be able to do after reading Chapter 11 Questions to think about
431 431
What is intelligence?
432
Theories of intelligence
432
Spearman’s two-factor theory Evidence from factor analysis Sternberg’s triarchic theory of intelligence Gardner’s multiple intelligences theory Emotional intelligence Estimating intelligence – An international perspective Are there consistent sex differences in cognitive ability? Sex differences in general knowledge
432 433 434 436 436 438 440 444
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Intelligence testing
444
12 Developmental psychology
Early intelligence tests Modern intelligence tests Reliability and validity of intelligence tests
444 445 447
What you should be able to do after reading Chapter 12 Questions to think about
493 493
The roles of heredity and environment
448
Developmental psychology
494
Cutting edge: Do you have to be smart to be rich? The meaning of heritability Sources of environmental and genetic effects during development Results of heritability studies If intelligence is inherited, how does inheritance occur? Giftedness Psychology in action: Can low intelligence be improved? IQ and nutrition Cutting edge: The effect of intelligence on health Controversies in Psychological Science: Is there a relationship between race and intelligence?
448 449
Prenatal development
494
Stages of prenatal development Threats to normal prenatal development
494 496
Physical and perceptual development in infancy and childhood
497
Controversies in Psychological Science: Does foetal learning exist? Brain development Does the environment affect brain development? Motor development Perceptual development
497 498 499 501 501
Intelligence, thinking and ageing
457
Ageing and cognitive ability What is ageing? Why does cognitive ability decline? Dementia Dementia of the Alzheimer type Clinical features of DAT Memory decline in Alzheimer’s disease Dementia and the novelist: the case of Iris Murdoch Treatment for DAT
457 457 460 462 462 464 465 467 468
Cognitive development in infancy and childhood
505
Development of memory Knowing where things are – spatial development at 2 years old The development of cognition: Jean Piaget Vygotsky’s sociocultural theory of cognitive development Developmental models of information processing in cognitive development
505
Thinking
468
Classifying Formal and natural concepts Deductive reasoning Syllogistic reasoning – An international perspective Inductive reasoning Logical errors in inductive reasoning Cutting edge: Who believes in spoon bending? Cutting edge: How eBay works Psychology in action: Jury decision-making Problem-solving Where in the brain does decision-making occur? Reasoning and the brain Creative thinking Cutting edge: Creativity and romance Case studies in creativity Controversies in Psychological Science: Are creativity and psychopathology related? Cutting edge: The key to creativity – shut up! Chapter review Suggestions for further reading Journals to consult Website addresses
449 451 453 453 454 455 455 456
468 469 471 472 474 474 477 478 478 480 481 482 482 484 484 485 487 487 489 490 490
507 508 513 514
Social and emotional development in infancy and childhood
516
Infant attachment The nature and quality of attachment Predictors of secure attachment Relationships with siblings Relationships with others Social organisation – An international perspective
516 518 519 520 520 521
Disorders of social cognition and emotion
521
Autism Cutting edge: Loneliness and autistic tendency Asperger’s syndrome Theory of mind – An international perspective Conduct disorder/attention deficit hyperactivity disorder Disorders of emotional regulation
521 523 525 525 526 526
Development of sex roles in childhood
528
Development of sexual identity
528
Moral development
530
Piaget’s theory of moral development Kohlberg’s theory of moral development Evaluation of Piaget’s and Kohlberg’s theories of moral development Alternative models of moral development
530 530 531 532
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Adolescence
533
Sexual behaviour
572
Physical development Sexual maturation Behavioural effects of puberty How do adolescents view puberty? Changes in leisure activities reflect the move into young adulthood Psychology in action: Adolescence and the internet Social development, peer relations and delinquency Friendship Psychology in action: Bullying Relations with parents
533 533 534 535
Effects of sex hormones on behaviour Sexual orientation Neurobiological correlates of sexual behaviour
572 573 575
Aggressive behaviour
576
535 536 537 537 538 539
Ethological studies of aggression Hormones and aggression Testosterone: status, relationships and empathy Imitation and aggression Psychology in action: Aggression at work
576 576 578 578 579
Adulthood: beyond adolescence
540
Emotion
580
Middle adulthood: a period of contentment? Parenthood Work Late adulthood and the menopause Old age Death and bereavement Chapter review Suggestions for further reading Journals to consult Website addresses
540 541 542 543 544 546 547 550 551 551
Basic emotions The biology of emotion Controversies in psychological science: What is the key to enduring happiness? Emotion – An international perspective Emotional experience: anger and disgust Using display rules Facial feedback hypothesis Cutting edge: A slump in mental fortune Facing emotion
580 581
Theories of emotion
595
Physiological theories Evolutionary theories Cognitive theories Cutting edge: Keeping your emotional distance Controversies in Psychological Science: Dark clouds gathering, sunny spells later ... Emotion without cognition? Chapter review Suggestions for further reading Journals to consult Website addresses
595 597 598 599
13 Motivation and emotion What you should be able to do after reading Chapter 13 Questions to think about
553 553
Motivation
554
Biological needs Physiology of reinforcement
554 555
Ingestion: drinking and eating
557
Thirst What starts a meal? What stops a meal? Sensory-specific satiety Obesity Psychology in action: The problem of obesity and its treatment Controversies in Psychological Science: Can the bitter gene cause obesity? How emotion affects food intake Cutting edge: Mood food Anorexia nervosa Bulimia nervosa Aetiology of anorexia and bulimia nervosa Body dissatisfaction in healthy and eating-disordered women Cutting edge: Body size, television size and other peoples attractive size Eating disorders – An international perspective
557 558 559 560 562
582 583 591 592 593 594 595
602 603 603 605 606 607
14 Personality What you should be able to do after reading Chapter 14 Questions to think about
609 609
Towards a definition of personality
610
Trait theories of personality
610
Personality types and traits Identification of personality traits Cutting edge: Personality and music preference Cutting edge: How extraverted is ‘
[email protected]’? Personality – An international perspective Stability of personality traits across the lifespan Cutting edge: Sex and profession differences in personality How we view ourselves in the past and the present Cutting edge: Do you get better looking each day?
610 611 612
562 567 567 568 568 569 569 569 571 572
613 615 616 617 617 617
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Heritability of personality traits
618
Neurobiological basis of personality Cutting edge: Personality and birth order Controversies in Psychological Science: The state you’re in
619 619 621
The social learning approach
625
Expectancies and observational learning Reciprocal determinism and self-efficacy Person variables Locus of control Controversies in Psychological Science: Do traits or situations best predict behaviour? Psychology in action: Personality and romance
625 625 626 626
The psychodynamic approach
630
The development of Freud’s theory Structures of the mind: id, ego and superego Defence mechanisms Freud’s psychosexual theory of personality development Further development of Freud’s theory: the neo-Freudians Evaluation of psychodynamic theory and research
630 631 632 633 634 635
The humanistic approach
636
Maslow and self-actualisation Evaluation of the humanistic approach
636 638
Assessment of personality
639
Objective tests of personality Projective tests of personality Controversies in Psychological Science: Are projective tests reliable and valid? Chapter review Suggestions for further reading Journals to consult Website addresses
639 640
627 629
642 643 645 645 645
15 Social cognition and attitudes What you should be able to do after reading Chapter 15 Questions to think about
647 647
Social psychology
648
Doing social psychology
648
Social cognition and social knowledge
648
Forming impressions of people Schemas and categories Group schemas and stereotypes When good intentions backfire: stereotypes, influence and behaviour Facing racial stereotypes Cutting edge: Sexist humour: does it make you sexist?
649 651 652 654 655 656
Conceptual and historical issues in psychological science
656
Self and identity
657
Self-knowledge Orientations of self-knowledge Self-awareness Types of self and identity Social identity Self motives Self-esteem Cultural differences in self and identity – An international perspective
657 657 659 659 659 660 660
Social inference
661
Causal attribution Implications and extensions of attribution theory Attributional biases Psychology in action: Attributional processes in relationships Heuristic judgements
661 662 662
660
665 666
Attitudes and attitude change
668
The nature of attitudes Attitudes and behaviour Attitude change and persuasion Cognitive dissonance Self-perception Chapter review Suggestions for further reading Journals to consult Website addresses
668 669 670 672 674 675 676 677 677
16 Interpersonal and group processes What you should be able to do after reading Chapter 16 Questions to think about
679 679
Social influence
680
Compliance Obedience Cutting edge: Milgram and obedience to authority, 2007 The social psychology of attribution – An international perspective Conformity The Stanford Prison experiment Minority influence
680 682 683 684 685 687 688
People in groups
689
The treatment of marginal group members and deviants Which is more important – the individual or the group? Social facilitation Social loafing Group decision-making Cutting edge: Creativity and brainstorming
690 690 691 692 693 694
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Psychology in action: The social psychology of drinking Leadership Negotiation, teamwork and leadership – An international perspective Crowds and social movements When crowds go wrong: football hooliganism
696 697 698 699 700
Intergroup relations and prejudice
701
Intergroup behaviour Prejudice Cutting edge: Being left out in the cold Under-representation of women in academia – An international perspective Cutting edge: Shoot me, I’m black Can we reduce prejudice?
701 704 704 706 707 709
Aggression and helping behaviour
712
Aggression Prosocial and helping behaviour Controversies in Psychological Science: What did Kitty Genovese’s witnesses really witness?
712 713
Attraction and relationships
Stress and health
749
Selye’s general adaptation syndrome The biological basis of stress Physiological mechanisms involved in stress Cognitive appraisal and stress Cutting edge: Going off the rails? Psychoneuroimmunology Cutting edge: Telomeres – what are they and can they predict stress? Stress and the immune system Controversies in Psychological Science: Can humour reduce stress? Psychology in action: The health benefits of saintliness – when it is better to give (and forgive) ...
750 750 751 752 753 753
762
Coping with everyday stress
764
716
Sources of stress Coping styles and strategies Do psychological interventions reduce stress? Chapter review Suggestions for further reading Journals to consult Website addresses
764 765 767 768 769 770 770
Interpersonal attraction Loving Maintaining and ending relationships
716 718 718
18 Abnormal psychology
Communication and language
719
What you should be able to do after reading Chapter 18 Questions to think about
773 773
Speech and language Computer-mediated communication Non-verbal communication Cutting edge: What’s in a name? Speech style The social psychology of gossip Cutting edge: I don’t mean to be rude, but ... Chapter review Suggestions for further reading Journals to consult Website addresses
719 719 720 720 721 722 722 723 724 725 725
CLASSIFICATION AND DIAGNOSIS OF MENTAL DISORDERS
774
What is ‘abnormal’?
774
714
17 Health psychology
755 756 757
The causes of mental disorders
774
The psychodynamic perspective The medical perspective The cognitive behavioural perspective The humanistic and sociocultural perspective The diathesis-stress approach
774 775 775 775 775
Classification of disorders
776
DSM-IV TVR classification Controversies in Psychological Science: How valid and reliable is the DSM?
777
The need for classification
779
Lay knowledge of mental illness Mental illness – An international perspective
780 780
What you should be able to do after reading Chapter 17 Questions to think about
727 727
Health psychology: a definition
728
Health and ill health
728
Nutrition Heart disease and eating – explaining the French paradox Physical fitness Controversies in Psychological Science: Can exercise improve mood? Cigarette smoking – An international perspective Psychology in action: How to stop smoking Alcohol use Sexually transmitted diseases and AIDS
728 729 730
THE TREATMENT OF MENTAL DISORDERS
782
The evolution of interventions
782
731 732 736 740 745
Controversies in Psychological Science: How violent are the mentally ill?
783
The development of modern treatment
784
777
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Current treatment: the eclectic approach
784
Schizophrenic disorders
814
Types of schizophrenia Psychology in action: Treating paranoid schizophrenia Aetiology Treatment Mood disorders
815 815 816 819 820
Mania
820
Depression
821
Description Aetiology Cutting edge: Cold summers, depressed Swedes and antidepressants Suicide – An international perspective Treatment
821 822
Types of treatment
785
Psychoanalysis and psychodynamic therapy Modern psychodynamic therapy Humanistic therapies Behavioural and cognitive behavioural therapies Psychology in action: How instructions to express reduce distress Other forms of psychotherapy Controversies in Psychological Science: Does psychotherapy work? Biological treatments
785 786 787 789
MENTAL DISORDERS
798
Anxiety, somatoform and dissociative mental disorders
798
Seasonal affective disorder (SAD)
829
Anxiety disorders
798
Generalised anxiety disorder (GAD) Panic disorder Phobic disorders Cutting edge: Phobias and reduction in cortisol Psychology in action: Virtual planes can relieve real fear of flying Post-traumatic stress disorder (PTSD) Obsessive-compulsive disorder
799 800 801 803
Sexual dysfunctions
829
Paraphilia
829
Psychology in action: Treating exhibitionism Chapter review Suggestions for further reading Journals to consult Website addresses
830 830 833 834 834
792 793 794 797
804 805 806
825 825 827
Somatoform disorders
808
Appendix: Understanding research results
Somatisation disorder Conversion disorder
808 808
Descriptive statistics Inferential statistics: are the results significant?
A1 A4
Dissociative disorders
809
Personality disorders
810
Antisocial personality disorder
810
Glossary References Indexes
G1 R1 I1
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Preface to the fourth edition
Here’s an apparently simple question: What made you pick up this book and read it? You might be a psychology student and spotted this book in your library or bookshop. It might be the recommended text on your course. You may have been at a friend’s house, become bored and begun leafing through this book lying on a table. You may have been attracted to the cover. You may even have liked the authors’ other books so much that you had to read this one as well. This simple exercise illustrates the essence of psychology – the scientific study of why and how humans (and animals) behave in the way that they do. Psychology is the science of behaviour and, being a science, it approaches the understanding of behaviour in a specific way. Everyone has an opinion on psychology and on what motivates people and what brings people to react and behave in the way that they do. We are all quasi-psychologists, in a way. Trained psychologists, however, attempt to understand behaviour through careful experimentation and empirical observation. They do this because it is the best method of gaining useful and reliable information about behaviour and the causes of behaviour. This book, the fourth edition of Psychology, introduces you to the scientific approach to understanding human behaviour and each chapter reviews the current state of knowledge about behaviour – from intelligence and emotion to child development and prejudice – based on sound scientific study. Let’s go back to the opening paragraph. The reason you are reading this book is probably because it was recommended on your psychology course or because you have spotted it in the library or bookshop and think that it will give you good value for money. As a student of psychology, you are studying the most fascinating and complex subject matter in science – human behaviour. You study not just how individuals develop language, perceive visual images, reason, feel, respond to others and learn, but also the biological bases of these behaviours. You will learn about the various methods that psychologists adopt when studying behaviour and how people evolved to do the things that they do (although scientists do have disagreements over the best method of study to adopt – the one certain fact you will learn in psychology is that no finding is ever ‘cut and dried’, there is always discussion and controversy). Psychology is one of the most popular degree courses in Europe and in North America – it is the third most popular degree subject in the UK, based on student applications to study. The subject matter is intrinsically interesting and its study allows students to develop what are called, in management-speak, ‘transferable skills’ – skills such as operating a computer, writing laboratory reports, producing clear and evaluative written work, performing statistical operations, using statistical software packages, designing projects, communicating,
material to an audience ... all of these, in addition to understanding specific aspects of human behaviour such as how children learn to read, why we perceive in the way that we do, how we influence others, how the brain works, how we reason and so on.
The fourth edition – pedagogical features The fourth edition of Psychology continues where the last three editions left off. It is designed to give you a flavour of what modern psychology is about. It describes every major field of psychology and includes up-to-date information and clear evaluation of controversial findings, theories and models in psychology. One of the best ways to learn about psychology is to keep abreast of new developments in the field. As a beginning student, you clearly need to know and understand the basics, but you also need to know how those basic findings are being modified and challenged. As a result, the new edition has over 430 new references, reflecting the extensive nature of the updated content and its emphasis on presenting you with upto-date information from the psychology research literature (it also reflects how prolific psychologists are). This fourth edition, like the previous three, has several features to help you understand the applications and controversies in psychology and to make you think more deeply about psychological issues and psychological research. Here’s a brief summary:
Conceptual and Historical Issues in Psychological Science Understanding the history of a discipline and the context in which research emerged is important for any discipline. Throughout the book, at the relevant point, a CHiPS symbol will appear next to the text which will flag up any issues related to a major conceptual or historical milestone in psychology. When you come across one of these icons, pause and think about issues surrounding the topic being described and evaluated.
An International Perspective Every chapter has a section headed ‘An International Perspective’, which allows you to see how psychology is, and has been, studied across nations and cultures. An important issue in psychological research is whether findings are universal or specific to a group being studied. If you find that someone behaves in a particular way in one group in one culture or country, would a similar person behave in the same way, under the same conditions in another culture or country? This section provides an international perspective on topics such as
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emotion, personality, memory, cannabis use, physical attraction, infidelity, sex bias, language and brain activation, prejudice, eating disorders, mental illness and many others.
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This will alert you to one of the major interactivities in MyLab, your online course in introductory psychology that helps you test your knowledge and understanding of the material in each chapter. The interactivities come in various forms – multiple choice questions, true or false questions. Most, however, will involve you applying your knowledge and understanding via interactive exercises. The chapters in MyPsychLab correspond to those in your book. When you are ready to explore the resources for a chapter you will need to log in to MyPsychLab, to the relevant chapter and click on to the study guide. From here, you can watch and work through animations, exercises, interactions, tests and much more to help further and consolidate your understanding.
Cutting Edge The Cutting Edge feature reviews a recent study or series of studies that are novel, important or make a really significant contribution to our knowledge and understanding of psychology. Some of these include research on: why celebrity worshippers worship (Chapter 1), how stories are more persuasive than statistics (Chapter 2), whether a woman’s fertility influences her acceptance of a date (Chapter 3), jealousy and brain activity (Chapter 3), the neurobiological correlates of behaving like James Bond (Chapter 4), predictors of university success (Chapter 7), the effect of chewing gum on memory (Chapter 8), how evening and morning types differ (Chapter 9), the role of the brain in interpreting irony (Chapter 10), the effect of intelligence on wealth and health (Chapter 11), how eBay works (Chapter 11), loneliness and autistic tendency (Chapter 12), how posture influences emotion (Chapter 13), how emotion affects food intake (Chapter 13), whether your email address reflects your personality (Chapter 14), whether different States show different personalities (Chapter 14), whether sexist humour makes us sexist (Chapter 15), how obedience to authority has not changed for decades (Chapter 16), the relationship between ostracism and our perception of our environment (Chapter 16), the relationship between your name and your success (Chapter 16), the role of telomeres in stress (Chapter 17), and the effect of commuting distance on stress (Chapter 17). There are 44 new Cutting Edge sections in this edition.
Controversies in Psychological Science Each chapter contains at least one section which focuses on a controversy in psychological science. The best advice I was given by one of my tutors as an undergraduate was, ‘question everything’. By this, he did not mean criticising studies or theories for the sake of it. He meant that psychology was a live, constantly evolving science
which, like all sciences, progresses by contradiction: somebody reports a finding; another refines this finding by showing that it applies only to certain contexts, people, conditions and so on. Most introductory texts can appear biblical: unquestionable towers of knowledge. But, although a great deal of fact is presented in this text, it also shows you how facts can be interpreted in different ways. The Controversies in Psychological Science sections are made up of three parts. The first part (the issue) outlines the controversy; the second part (the evidence) describes and evaluates the data that give rise to the controversy; finally, the third part (conclusion) briefly suggests what we can conclude from the evidence available. One aim of the Controversies in Psychological Science sections is to engage you in critical thinking by presenting you with a controversial topic, theme or idea in psychology and take you through evidence for and against a topic, theme or idea. Some of these controversies are well known: Is intelligence racially determined? Can primates learn language? Are psychiatric patients violent? Others are not so well known but cast some light on some aspect of psychology and behaviour: Is psychology common sense? Does the weather influence mood and thinking? Do ‘smart’ drugs work? Can neuroimaging detect deception? And so on. The material covered in the Controversies sections will give you a hint of the liveliness of debate surrounding some issues in psychology and could form the basis of discussion with your fellow students or with colleagues in tutorials or seminars.
Psychology in Action Research in psychology is aimed at exploring, defining and predicting the causes of behaviour. Some of it is also aimed at using such research in an applied, practical setting. The Psychology in Action sections review the evidence for the application of psychological principles to a ‘real-life’ issue: for example, using closed-circuit television (CCTV) to identify criminals; jury decision-making; road traffic accident reduction; the use of brain technology to help the seriously ill to communicate; differences between men and women in the ways they use language, and so on. Chapter 18 on mental disorders is almost a whole PiA section in itself because it describes the study and treatment of mental illness. These sections aim to show you how principles from psychology can be used to help us to understand why we behave in the way that we do.
What you should be able to do after reading the chapter At the beginning of each chapter there is a brief description about what you should be able to do after reading the chapter. This section provides you with a set of goals that you should try to achieve during the course of reading the chapter. The items in these sections are, in essence, your learning objectives.
Questions to think about The beginning of each chapter also presents you with a series of questions to think about. The Questions to Think About feature has been designed to help you ask questions about your knowledge of
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psychology and to probe what you have learned from the topic you have read. There are further questions for you to think about embedded throughout each chapter.
Chapter reviews At the end of each chapter there is a summary of the information that has gone before. The summary has been bullet-pointed to make it easy to read and understand.
Glossary Important terms that are defined in the text and which appear in bold also appear, alphabetically, in a glossary at the end of the book.
Suggestions for further reading As an intelligent reader of an introductory textbook you will be hungry for more psychological knowledge after having tasted this starter. The suggestions for further reading are designed to satisfy your appetite. All the recommended readings come with comments and these should help you to decide on what further reading is best for you. Some of the reading is quite advanced; other readings are less demanding. You should try to consult at least a few of these per chapter because the further reading will lead you into more detailed description and discussion of psychological topics.
Journals to consult In addition to the further reading, we have added a list of journals for you to consult. About 90 per cent of the facts, theories and ideas that you read about in this book have been published in science journals and there are many different types of journals in psychology. This is where original research, theories and methods in psychology are published. If you want to go direct to the source of psychological research then journals are the place to go. You might find much of the material in them deeply unattractive, incomprehensible or abstruse. However, you will also find material that is original and new. Textbook
authors are a little like journalists reporting the events and people that they think readers will be interested in. Of course, textbook authors have few of the failings of journalists but they can only give you a brief glimpse of the events that they report. The beauty of psychology is that you can consult the source yourself, and the journals listed should help you do this.
Website addresses Following the annotated suggested reading, we have included, for each chapter, the internet addresses of some websites which are worth visiting. Some of these give you more information about the general or specific issues raised in the chapter; some provide you with online tutorials, experiments, virtual libraries or bibliographies. All of these features, together with the extensive revision of the text to make it up-to-date and comprehensive, should provide you with an effective learning tool. To familiarise yourself with these features and how they will benefit your study of this text, they are reproduced and described in the guided tour which follows. I very much hope that you will learn a lot about psychology from the fourth edition of Psychology. I also hope that you enjoy what you learn and that the book will take you to places you had not thought of exploring. This is the beauty of psychology. Opening one door will lead you to several others. If you like what you have read, then please do let me know. One of the joys of teaching and researching is obtaining feedback about the work that you produce. If you have any comment to make or suggestion for improvement, then please write to me, G. Neil Martin, Department of Psychology, School of Health and Social Sciences, Middlesex University, The Burroughs, Hendon, London, NW4 4BT, UK, or email me at:
[email protected]. You can also visit my website at: http://www.mdx.ac.uk/hssc/staff/profiles/academic/ martinn.htm. G. Neil Martin, FRSA London, 2009
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Luck can change your life Ms V is a compulsive gambler. It wrecked her marriage and drained her wallet long ago. Her kids don’t like her because she is always barely scraping by – and borrowing money from them – waiting for the next big win that she hopes will give her all the cash she needs to escape her current mess. How did it all begin? The answer lies in the schedules of reinforcement. At college, one of her boyfriends
This book is accompanied by MyPsychLab, which contains a wealth of interactive learning tools to enrich your experience of the text, including a study plan, multiple choice questions, animations, interactions and questions. Log on to http://www.mypsychlab.co.uk and follow the registration instructions inside the access card at the back of this book to access these valuable resources.
liked to bet on the horses and V went along one day. She bet £10 on a filly named Flo and won £300. What a rush! Luck brought her a giant reinforcer without much effort – with no ‘down side’ in sight. Her boyfriend was excited, too. V saved the money and went back to the track several more times over the next several weeks – sometimes alone, sometimes with her boyfriend – making more £10 bets. Most lost. A few made small wins. But the betting was exciting, and there was lots of sensory stimulation when her horse took one of the front positions. When V’s £300 was about half gone, she bet on a long shot with big odds. No one expected Viceroy to win, but V put down £75 on a hunch. Viceroy. . . won by a nose. V walked away with £4,500 in her pocket. Early periods of generous reinforcement can have a big effect on our later behavioural decisions. Source: adapted Baldwin and Baldwin (1998)
CHAPTER 7
Guided tour
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 7
• Describe the concept of habituation and the phenomena of classical conditioning and operant learning.
• Understand the principles underlying classical conditioning.
• Understand the principles underlying operant conditioning.
• Describe and explain conditioned aversions. • Describe the nature of insight. • Apply the principles of learning theory to behaviour. • Describe some of the factors that influence academic learning.
QUESTIONS TO THINK ABOUT
• Do different aspects of learning have different underlying
•
• What factors do you think enhance and promote the process of learning?
principles? Is learning to ride a bike governed by different principles from those used for learning to find your way around college or university or learning a foreign language?
• What psychological factors can enhance (or impair) your
Does all learning have to be intentional? Can you learn something without knowing it or without wanting to learn it?
• In what way is the brain like a computer (and vice versa)?
academic learning?
• Is learning a process that depends on innate ability, the ability to adopt successful learning strategies or both? Explore the accompanying video, simulations, and animations on MyPsychLab. This chapter includes activities on: Acquisition of conditioned responses • Stimulus generalisation and stimulus discrimination • Classical conditioning of Little Albert • Schedules of reinforcement • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available
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Psychology in action – Continued
(a) Leonard Shelby, played by Guy Pierce in the film Memento, is one of the few successful cinematic portrayals of amnesia. The most successful, however, appears to be Dory (b) , in Finding Nemo. Source: (a) Summit Entertainment/The Kobal Collection Ltd; (b) W. Disney/Everett/Rex Features.
sticky strings spurting from his wrists, to cheer for a group of hobbits, to boo an asthmatic, black-helmeted villain, or to see a boy in spectacles racing on a broom in a flying contest. Reality becomes important, however, if the reality is meant to be accurately portrayed. Dustin Hoffman’s character in Rain Man, for example, although an extreme example, is an
The role of the hippocampus in memory ee
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Each chapter of Psychology begins with an extract introducing you to the topic by using a real world example. Questions to think about encourage you to reflect on the key issues in the chapter, while the list of What you should be able to do helps you to track your learning as you read. The MyPsychLab feature also suggests some of the interactive resources available to support your understanding of these topics. [
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The hippocampus, like many structures of the brain, is not fully mature at birth. In fact, it is not until a child is 2–3 years old that most of these structures are fully developed. As a result, many cognitive activities, such as the formation of semantic memories, are not particularly well developed until this age (Liston and Kagan, 2002). One reason that few people remember events that occurred during infancy may be the immaturity of the hippocampus. The hippocampus receives information from all association areas of the brain and sends information back to them. In addition, the hippocampus has two-way connections with many regions in the interior of the cerebral hemispheres. Thus, the hippocampal formation is in a position to ‘know’ – and to influence – what is going on in the rest of the brain (Gluck and Myers, 1995). Presumably, it uses this information to influence the establishment of explicit long-term memories. The structure appears to be very important for navigating or exploring our way around a spatial environment or in forming representations of the locations of objects (O’Keefe and Nadel, 1978). Morris et al. (1982), for example, placed rats in a pool of milky water that contained a platform just underneath the water. yp
attempt at a serious portrayal of the social debilitation experienced by a person with Asperger’s Syndrome. (The man who inspired the Hoffman character appears in Chapter 12.) The general lesson, however, is this: don’t go to the movies expecting to learn much about psychology. In fact, as this section demonstrates, you might as well forget it. . .
In order to avoid swimming constantly, the rats had to find the platform hidden beneath the milky water. Eventually, through trial and error, the rats would find the platform. Then, the researchers performed a series of experimental ablations. One group of rats received lesions to the hippocampus, another received lesions to the cerebral cortex and another received no lesion. When the rats were then allowed into the pool, the pattern of behaviour seen in Figure 8.21 was observed. Notice how those rats with the hippocampus lesion had extremely poor navigation compared with the cortex lesion and control group. Similarly, when rats had learned that there was a platform under water and were then allowed to explore the water with the platform removed, those with an intact hippocampus would spend longer in the part of the maze where the platform had been previously positioned. Those rats with hippocampal lesions, however, did not engage in this ‘dwell time’ in the quadrant where the platform once was (Gerlai, 2001). This suggests an important role for the hippocampus in spatial learning. Both rodents and primates show deficits in what has been called spatial memory (Redish and Touretzsky, 1997). Spatial memory, the ability to encode and retrieve information about locations and routes is, like memory itself, not a unitary function. Kessels et al. (2001), for example, note that there is a difference between memory
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This new edition is richly illustrated with diagrams and photographs.
VISION
Psychology in action – Red light = danger?
Psychology in action uses fascinating, real-life examples to show how psychology is applied in the real world.
British psychologist Hans Eysenck noted in this chapter’s opening quote, most people believe that they are experts in human behaviour. And to some extent we are all lay scientists, of a kind, although generally unreliable ones.
According to some anthropologists, the colour red is seen as a sign of dominance in non-human species. Of course, what applies in the animal kingdom does not necessarily apply to the human kingdom. A study from researchers at the University of Durham, UK, however, suggests that it might. In a novel study, the researchers examined the success and failure of sportsmen and women who wore red or blue costumes (Hill and Barton, 2005). In the 2004 Olympic Games, contestants in the combat sports, boxing, tae kwon do, GrecoRoman wrestling and freestyle wrestling, were randomly given either red or blue costumes to wear. When Hill and Barton (2005) analysed the win rate of contestants, those in red costumes won more fights than those in blue costumes. They then further extended this research by examining the win rate of players in the Euro 2004 international football competition. The performance of five teams that wore red was compared with the performance of the same teams when they wore a different colour. Again, the study’s finding was novel: the team won more often when wearing red shirts. According to the authors, ‘given the ubiquity of aggressive competition throughout human societies and history, our WHATthat IS PSYCHOLOGY? results suggest the evolutionary5 psychology of colour is likely to be a fertile field for further investigation’. Psychological research, however, frequently contradicts The effect of the colour red even seems to extend to cognipeople’s assumed expertise as section- exposed students to either tivethe testControversies performance. Researchers below illustrates. the colour red, green or black before giving them a test. Participants who were exposed to red – even if participants were not consciously aware of it – performed less well on a test than did those who were not (Elliot et al., 2007). The effect was found even when a number was written in red ink at the top of a sheet of paper. When participants’ brain activation was examined, there was greater activation in the right references in journal articles were recent; the age at which a side of the frontal lobe when seeing the colour red (a theory, person received the Nobel prize; and perceived difficulty of described in Chapter 13, argues that the left and right front the discipline. Simonton combined these measures to provide parts of the brain mediate different kinds of emotional experia composite measure of scientific status. ences, positive and negative respectively). Based on the first set of indicators, Simonton found that But some psychologists have questioned this influence of the natural sciences were judged to especially be more ‘scientific’ than red, that seen in the sport studies. For example, it were the social sciences. Psychology onthat the the mean – itself did not influence the could fell be right argued colour at the junction between natural and social sciences, Figure chances of winning butasthat fact that red was more highly visible
in the sports studied (Rowe et al, 2005). Some have also questioned the bias of the referee. The colour might influence the perception of performance, regardless of actual performance. In an ingenious test of this hypothesis, Hagemann et al., (2008) asked 42 experience tae kwon do referees to watch a videotape of five different sparring competitions. The competitors’s heads and trunk were covered in red or blue material. When asked to award points to these competitors, the red ones were given 13 per cent more points (as previous research would predict). Then, and this is the ingenious twist, the experimenters electronically switched the colours of the competitors – the actual competitors remained the same, as did their performance, but the colour they wore changed. When this happened, the points awarded to the red competitors increased. Those who had been given the points in the previous study (and were now dressed in blue) were awarded fewer. These results, according to the authors, suggest ‘need a change to the rules (i.e., to forbid red sports attire) and support referees by providing electronic-decision making only’.
Cutting edge – How much of a science is psychology?
Cutting edge introduces you to some of the most interesting new subjects of study in contemporary psychology.
• the number of theories and laws mentioned in introductory textbooks (the higher the ratio of theory to law, the ‘softer’ – i.e. less scientific – the discipline); • publication rate (the more frequent, the more scientific the discipline); • the appearance of graphs in journal papers (the ‘harder’ the discipline, the greater the number of graphs); • the impact made by young researchers (the more scientific the discipline, the greater the agreement that a researcher’s contribution is significant); • how peers evaluated 60 of their colleagues in their own disciplines, and how often single papers are cited (referred to in research papers). Simonton also looked at other measures of scientific standing: ‘lecture disfluency’ (the number of pause words such as ‘uh, ‘er’ and ‘um’: these are more common in less formal, less structured and less factual disciplines); the extent to which
1.1 shows. However, psychology’s score was much closer to biology than to sociology. The biggest gap in scores was found between psychology and sociology, suggesting that the discidimension to their colour vision. A study of women with pline is closer to its natural science cousins than its social a phenotype expressing four photopigments found that science acquaintances.
Composite score
Psychology is a young science and the discipline has tried hard to earn and demonstrate its scientific spurs. Chemistry, physics or biology seem to have no such problems: their history is testament to their status as a science. A new study, however, suggests that psychology is gaining ground. Simonton (2004) compared the scientific status of psychology with that of physics, chemistry, sociology and biology. He identified a number of characteristics that typified a general science including:
this was the case: these people perceived more chromatic appearances than did male or female trichromats (Jameson et al., 2001). Two of the three colour defects described below Physics involve the red/green system. People with these defects confuse red and green. Their primary colour sensations
1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 –0.1 –0.2 –0.3 –0.4 –0.5 –0.6 –0.7 –0.8 –0.9 –1.0 –1.1
Does the colour of a team’s kit influence their success? Source: Chris Coleman/Manchester United
are yellow and blue; red and green both look yellowish. Figure 5.22 shows one of the figures from a commonly used test for defective colour vision. A person who confuses red and green will not be able to see the ‘5’. The most serious defect, called protanopia (literally, ‘first-colour defect’), appears to result from a lack of the photopigment for red cones. The fact that people with protanopia have relatively normal acuity suggests that
Chemistry
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Psychology
Sociology
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(a)
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The stereotypical image of a psychologist (a) and a traditional scientist (b).
Source: D.K. Simonton, ‘Psychology’s status as a scientific discipline: its empirical placement within an implicit hierarchy of the sciences’, Review of General Psychology, 2004, 8, 1, p. 65 (Fig. 2).
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Source: (a) Pelaez Inc./Corbis; (b) Tomas de Arno/Alamy Images.
Figure 1.1 According to Simonton’s study, psychology’s scientific status was more similar to that of biology than other disciplines traditionally associated with it, such as sociology.
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Suicide – Continued Suicide attempts in adolescence are associated with heavy or frequent drinking and illegal drug-taking (Shaffer and Pfeffer, 2001; Gould et al., 2003). A group of Norwegian researchers monitored the correlation between substance use and suicide in two surveys (in 1992 and 2002) of 23,000 13–19-year-olds
An International Perspective allows you to explore global differences in psychological research, attitudes, policies and methods.
(Rossow et al., 2005). There was a significant relationship between increased substance use and suicide, but only in girls. For boys, the effect of substance use seemed to be less pronounced in 2002 than in 1992. For both sexes, the substance most significantly associated with suicide attempts was alcohol.
Reported (1950–1995) and estimated (2020) suicide rates in reporting countries
Age distribution of suicide between 1950 and 1998
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10 5 0 1950
1950 (11 countries) 1995 900,000 deaths reported
2020 1.53 mio. deaths estimated
To be a true psychologist it is vital to understand the conceptual and historical issues that shape the field. Watch out for this icon as you read, which will help you remember key milestones in the development of psychological science.
Figure 18.9 World Health Organisation statistics for suicide rates across the world Source: World Health Organisation
5–44 years
1988 (50 countries) 45+ years
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Controversies in Psychological Science – Does mobile phone use impair your driving? The issue The sale of mobile phones has been one of the marketing successes of the past few years: approximately 1 billion of them were in use worldwide in 2002 and it is estimated that 2.6 billion will be in use by the end of 2009. Mobile phones are portable, convenient and handy. So handy, that people often use them while doing other things. Surveys suggest that around 80 per cent of mobile phone users report having used the device while driving, despite the use of such devices being illegal in many countries (Goodman et al., 1999). In 2003, for example, the UK passed an amendment to the Road Vehicles Act which made it an offence to drive a motor vehicle on a road while using a handheld telephone (although not hands-free sets). The rationale for the ban is that factors such as holding the phone or dialling a number cause significant distraction and lack of control over the vehicle. Is there scientific evidence for this assumption?
The evidence Strayer and Johnston (2001) have suggested that it is not the physical handling of mobile phones that leads to accidents but the conversations people have on them. They measured the errors made by drivers in a simulated driving task. These drivers either listened to a radio, listened to a book on tape, performed a word shadowing exercise on a mobile phone, held a conversation on a mobile phone or held a conversation using a hands-free set. The authors cite previous studies that have shown a relationship between phone use and driving accidents. Redelmeier and Tibshirani’s study (1997) of the phone records of those involved in driving accidents found that 24 per cent of people used their
A hands-free set causes less distraction than a hand-held phone, when driving, but research suggests that it is the conversation you have that causes inattention’
New Controversies in Psychological Science examine recent reports and beliefs about psychological findings, to help develop your skills in critical analysis.
phones within the 10 minutes before the accident. They argued that this rate suggested a danger that was as great as having excess alcohol in your bloodstream. Strayer and Johnston suggest that while the relationship appears causal, there may be other factors, such as the personality and disposition of the drivers, which caused the accident. Furthermore the study did not consider the conversational aspect of telephone use, although a study by Briem and Hedman (1995) suggested that holding a simple conversation did not significantly impair the ability to stay on the road. Strayer and Johnston tested two hypotheses. The peripheral-interference hypothesis attributes driving accidents to non-conversational uses of the mobile phone such as holding and dialling. The attentional hypothesis attributes any driving impairment to the nature of the conversation taking place on the mobile phone. In their simulated driving experiment, 48 undergraduates used a joystick to operate a cursor which they moved to follow a moving target on a computer screen. The target would move unpredictably, although not suddenly. Sporadically a green or red light would appear. If a green light appeared, the participant was asked to continue; if the red light appeared they were told to press a button which represented the brake on the joystick. The participants either conversed with a confederate on a mobile phone – they discussed President Bill Clinton’s potential impeachment, and the Salt Lake City Olympic Committee bribery scandal – or conversed with a hands-free set or listened to a radio broadcast (which they could choose). The researchers found that the probability of missing a red light almost doubled when participants talked on the phone – whether hands-free or hand-held – compared with when they listened to the radio. There was no significant difference in the error rate between the two phone groups. Not only was the miss rate higher in these two groups, they were also slower to respond to the lights, as Figure 9.5 shows. People drove more poorly during the ‘talking’ portion of the conversation than the ‘listening’ portion. To check that participants were listening to the material in the control condition – the authors did not assess this in their first experiment – and to ensure that the control condition was speech rather than music and speech-based, a second experiment required participants to complete the same simulated driving task but one group listened to a book on tape. This group did not perform significantly worse than the phone groups, suggesting that attending to verbal material is not enough to impair driving: active engagement in conversation is necessary for errors to be committed.
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Source: Corbis/Juice Images
CHAPTER REVIEW
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Chapter review Prenatal development
Cognitive development in infancy and childhood
• The three stages of prenatal development span the time
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between conception and birth. In just nine months, the zygote grows from a single cell, void of human resemblance, into a fully developed foetus, complete with physical features that look much like yours and mine, except in miniature. Sex is determined by the sex chromosomes. Male sex organs are produced by the action of a gene on the Y chromosome that causes the gonads to develop into testes. The testes secrete androgens, a class of hormones that stimulates the development of male sex organs. If testes are not present, the foetus develops as a female. The most important factor in normal foetal development is the mother’s nutrition; malnutrition leads to abnormal development and impaired cognition. Normal foetal development can be disrupted by the presence of teratogens, chemicals which can cause mental retardation and physical deformities; one teratogen is alcohol – when consumed by a pregnant woman, this may lead to foetal alcohol syndrome. There is evidence that the human foetus is capable of discriminating between sensory stimuli while in the womb, suggesting that it is capable of a rudimentary form of cognition.
Physical and perceptual development in infancy and childhood
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to its survival. For example, the rooting, sucking and swallowing reflexes are important in finding and consuming food. Sophisticated movements, such as crawling and standing, develop and are refined through natural maturation and practice. A newborn’s senses appear to be at least partially functional at birth. However, normal development of the senses, like that of motor abilities, depends on experience. The brain appears to develop throughout infancy and adolescence, with myelination being the key characteristic of maturation. Because the infant lacks language, most studies of motor and perceptual development examine the child’s non-verbal response to stimulation. These responses include movements involving the head, mouth and eyes. If an infant is deprived of the opportunity to practise them during a critical period, these skills may fail to develop, which will affect the child’s performance as an adult. Before the age of 2 years, infants seem to be more concerned with the contours of visual stimuli – a phenomenon called the externality effect.
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many events are contingent on its own behaviour. This understanding occurs gradually and is controlled by the development of the nervous system and by increasingly complex interactions with the environment. By around 3 months, the infant shows awareness of changes in its environment; by 6 months, it is able to remember temporal order of stimuli. At 8 months, it is able to recognise words spoken in a story that it heard a while before. Over the course of development from 1 to 2 years the number of sequences of actions that the child can remember increases. Three factors seem to account for the child’s ability to recall information better with age: the formation of memory-related structures, the development of language, and the development of metamemory – the realisation that using memory strategies will help the child to think and behave. According to Piaget, as children develop they acquire cognitive structures – mental representations or rules that are used for understanding and dealing with the world and for thinking about and solving problems. The two principal types of cognitive structure are schemata (mental representations or sets of rules that define a particular category of behaviour) and concepts (rules that describe properties of environmental events and their relations to other concepts). According to Piaget, two processes help a child to adapt to its environment: assimilation, the process by which new information is modified to fit existing schemata, and accommodation, the process by which old schemata are changed by new experiences. Piaget divided a child’s cognitive development into four periods – a system that is widely, if not universally, accepted. These periods are determined by the child’s experiences and the maturation of its nervous system. An infant’s earliest cognitive abilities are closely tied to the Personality reading external stimuli in – thegeneral immediate environment; objects exist for theAllen, infantB. only whenPersonality they are present (theDevelopment, sensorimotor growth period).and (2006) Theories: Gradually, infants learn that objects exist even when hidden. diversity (5th edn). Harlow: Pearson Education. C.S. andofScheier, M.F. (2008) Perspectives on Personality TheCarver, development object permanence leads to the ability to (6ththings edn). Boston: Allyn which & Bacon. represent symbolically, is a prerequisite for the Cloninger, S.C. (2008) Theories of Personality (5th edn). Boston: use of language (the preoperational period). Prentice Next, the abilityHall. to perform logical analysis and to understand Costa, P.T. and McCrae, R.R. (2005) Personality in Adulthood. New more complex cause-and-effect relations develops (the period York: Guilford Press. of concrete operations). Gregory, R.J. (2007) Psychological Testing (5th edn). Boston: Allyn Around&the age of 11 years, a child develops more adult-like Bacon. cognitive abilities abilities that may allow child toorigins solve of Lombardo, G.P.–and Foschi, R. (2002) Thethe European difficult problems by means of abstract reasoning (the period ‘personality psychology’. European Psychologist, 7(2), 143–5. of formal operations). Mischel, W. (2004) Toward an integrative science of the person. Annual Review of Psychology, 55, 1–22. Monte, C.F. and Sollod, R.N. (2002) Beneath the Mask (7th edn). Chichester: Wiley. Pervin, L.A. (2002) The Science of Personality. Oxford: Oxford University Press. Each of the titles in these two sections is a very good introduction to personality.
The extensive Chapter review enables you to consolidate what you’ve just learnt and is a great tool to help you revise.
WEBSITE ADDRESSES
Suggestions for further reading
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Issues and controversies in personality research Canli, T. (2006) Biology of Personality and Individual Differences. Hove: Psychology Press. Eysenck, H. (1985) Decline and Fall of the Freudian Empire. London: Pelican. Matthews, G., Deary, I.J. and Whiteman, M.C. (2003) Personality Traits (2nd edn). Cambridge: Cambridge University Press. McCrae, R.R. (2004) Human nature and culture: A trait perspective. Journal of Research in Personality, 38, 3–14. Pervin, L. (2002) Current Controversies and Issues in Personality (3rd edn). Chichester: Wiley. Zimmer, C. (2005) The neurobiology of the self. Scientific American Mind, 93–101. Zuckerman, M. (2005) Psychobiology of Personality (2nd edn). Cambridge: Cambridge University Press. Special issue of The Psychologist on ‘Freud’s Influence’, 2006, 19, 9.
Journals to consult British Journal of Psychiatry
Journal of Research in Personality
British Journal of Psychology
Perceptual and Motor Skills
European Journal of Personality
Personality and Individual Differences
European Psychologist
Personality and Social Psychology Bulletin
International Journal of Psychology
Psychological Reports
Journal of Personality
Psychological Science
Journal of Personality and Social Psychology
Website addresses http://pmc.psych.nwu.edu/personality The Personality Project at Northwestern University website. This excellent site has links to further reading, personality descriptions, related websites and much more. http://www.personalityresearch.org/ The Great Ideas in Personality website provides an account of exactly that.
http://www.psychology.org/links/Environment_Behavior_ Relationships/Measurement/ A collection of links to psychological testing and test sites. http://www.psychology.org/links/Environment_Behavior_ Relationships/Disposition-Personality/ A collection of links to personality sites.
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At the end of each chapter, Suggestions for further reading, Journals to consult and Website addresses provide links to further sources of information, allowing you to broaden your understanding of the topic and providing a great starting point for your own research.
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MyPsychLab walkthrough
Log in to http://www.mypsychlab.co.uk to access all the additional learning materials that accompany Psychology, Fourth Edition.
Study Plan The Study Plan section of MyPsychLab is a comprehensive self-test and revision centre. When you log in to MyPsychLab you can select any chapter and take a ‘pre-test’, to check how well you understand the topics in that chapter. This identifies any areas you need to work on and generates a personal study plan to help you learn. You can then take a ‘post-test’ after revising the study materials in more depth, to check your progress. The study plan includes: • Pre-test and post-test questions • Learning resources including simulations, animations and video • ‘Quick review’ revision questions • eText
Also accompanying the Fourth Edition of Psychology are a range of additional resources to help you learn and revise, such as twice-yearly research updates to provide access to the latest psychological literature.
Each chapter contains a large bank of multiple choice questions allowing you to test your knowledge of every topic within the book.
Flashcards are available for all key terms in the book, as well as an easy-to-access online glossary.
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Media Library The MyPsychLab Media Library contains a wealth of chapter-specific, rich learning resources to help you assess your knowledge and master key concepts.
Video Watch video clips of key experiments and phenomena in psychology and test yourself on what you have observed.
Simulations Interactive activities that test your understanding in a practical way.
Animations Fun and interesting animations allow you to watch psychology in action.
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The teaching package
For lecturers a range of supplementary materials is available to help you to plan lectures, create customised tests and set additional, tracked assignments for students. This package includes: Instructor’s Manual PowerPoint® Slides MyPsychLab with additional assignments MyTest testbank
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The authors
Dr G. Neil Martin is Reader in Psychology at Middlesex University, UK, a Chartered Scientist, and a Fellow of the Royal Society of Arts. He was educated in Wales, Scotland and England, graduating with a first-class Master of Arts degree in psychology from the University of Aberdeen, where he also won the annual Henry Prize for outstanding undergraduate achievement in psychology. He completed his Ph.D. on psychophysiology and olfactory perception at the University of Warwick, England. He is the author of Psychology – A Beginner’s Guide (Oneworld, 2008); Human Neuropsychology, the first European textbook in the field now in its second edition (Pearson Education, 2006); Essential Biological Psychology (Hodder Arnold, 2003); Study Guide – Psychology, with Nicky Brunswick (Pearson Education, 2005); and the 6th and 7th international editions of Psychology, with Neil Carlson and colleagues from the US and Canada (Allyn & Bacon, 2006, 2009). With Nicky Brunswick, he wrote the first European online course in introductory psychology (Pearson Education, 2001, 2003), now in its third edition (Pearson Education, 2006). He is the author of over 150 articles on psychology, has contributed to the Oxford Companion to Food, and acts as consultant to industry, business and the media on the psychology of olfaction and humour. He has been an editorial board member of The Psychologist, Journal of Health, Social and Environmental Issues and the Annals of Improbable Research – the satirical journal which awards the annual IgNobel prizes for science that should never be repeated – for which he is also a columnist. He also works as a freelance journalist; his first article for a major national newspaper was entitled ‘More than 20 things you needed to know about the nose’. Dr Neil R. Carlson is Professor of Psychology at the University of Massachusetts, USA. He studied as an undergraduate and postgraduate at the University of Illinois. He wrote his first textbook, Physiology of Behavior, while on sabbatical leave at the University of Victoria in British Columbia. He was the first Allyn & Bacon author to submit a book manuscript on a computer disk.
A few years ago he began to collaborate with Jay Alexander, an artist who works as a laboratory technician at the University of Massachusetts. They prepare all the artwork for Professor Carlson’s books. Dr William Buskist is Professor of Psychology at Auburn University, USA, where he regularly teaches the introductory psychology and the teaching of psychology courses. He has directed Auburn’s psychology research laboratories. He also teaches seminars and workshops for undergraduates who are preparing for graduate study in psychology. He graduated from Brigham Young University in 1981 with a Ph.D. in experimental psychology. Although most of his research has been in the area of human social behaviour, particularly competitive behaviours, Dr Buskist’s research now largely focuses on issues in the teaching of psychology. Dr Michael Hogg is Professor of Social Psychology at Claremont Graduate University, USA, and is a Fellow of the Society for the Psychological Study of Social Issues, the Society for Personality and Social Psychology, and the Academy of the Social Sciences in Australia. He was the foundation director of the Centre for the Study of Group Processes at the University of Queensland, and in 2004 he was a British Academy Visiting Professor at Birmingham University. Educated at Bristol Grammar School and the University of Birmingham, he received his Ph.D. in 1983 from Bristol University, and has held teaching posts at Bristol University, Macquarie University, the University of Melbourne, the University of Queensland, and Princeton University, and visiting appointments at the University of California, Los Angeles, the University of California, Santa Cruz, the University of California, Santa Barbara, City University, Hong Kong, and the University of Kent, UK. Michael Hogg’s research on group processes, intergroup relations, social identity, and self-conception is closely associated with the development of social identity theory. He has published over 200
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THE AUTHORS
scientific books, chapters and articles on these topics. With Graham Vaughan he is the author of Social Psychology – one of the leading introductory social psychology texts in Europe and the UK, it was first published in 1995 and is now in its fifth edition. An associate editor of the Journal of Experimental Social Psychology, Michael Hogg serves on the editorial board of most of the main social psychology journals, and is foundation co-editor with Dominic Abrams of the journal Group Processes and Intergroup Relations, and senior consultant editor for the Sage Social Psychology Program. This current research focuses on leadership, deviance, uncertainty reduction, extremism, and subgroup relations. Michael Hogg lives in Los Angeles, but spends substantial time each year in the UK, and in Brisbane, Australia. Dr Dominic Abrams is Professor of Social Psychology and Director of the Centre for the Study of Group Processes at the University of Kent, Canterbury, UK. He is a Chartered Psychologist, Fellow of the Society for the Psychological Study of Social Issues, and of the Academy of Social Sciences. Following his undergraduate degree at Manchester University and a Masters at the London School of Economics and Political Sciences, he received his Ph.D. in 1984 from the University of Kent, and held teaching posts at the universities of Bristol and Dundee before returning to Kent in 1989. He has held visiting appointments at the universities of Melbourne, Queensland and Urbana-Champaign, Illinois. This research on intergroup relations and the self-concept has concentrated on social identity, and spans childhood to old age, and
groups defined by gender, ethnicity, language, faith, sexuality and disability. He has been associate editor for the British Journal of Social Psychology, and special issue editor for the Journal of Community and Applied Psychology and the International Journal of Behavioral Development. He is foundation editor, with Michael Hogg, of Group Processes and Intergroup Relations, and serves on the editorial boards of Journal of Personality and Social Psychology and the European Review of Social Psychology. He has recently been chair of the British Psychological Society Research Board, and now chairs the Joint Committee for Psychology in Higher Education in the UK. His current research focuses on the social psychology of social inclusion and exclusion, societal indices of prejudice, the development of group understanding, and the role of intergroup contact in prejudice reduction. Dr Nicky Brunswick is Senior Lecturer in Psychology at Middlesex University, UK. She studied for her Ph.D. in the psychophysiology of dyslexia at the University of Warwick and completed her postdoctoral training with Chris and Uta Frith at the Wellcome Department of Cognitive Neurology, Institute of Neurology, London. She researches in the areas of health psychology and developmental dyslexia and her research on reading and dyslexia has appeared in the journals, Brain, Nature Neuroscience and Science. She is the author of Dyslexia – A Beginner’s Guide (Oneworld, 2009).
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Acknowledgements
In the course of writing and revising Psychology, I have had the good fortune to call on the expertise and detailed knowledge of a number of people. These include colleagues who reviewed my proposal for a revision of this text, members of Prentice Hall Europe’s Special Editorial Board for the first edition of Psychology, and my colleagues at Middlesex University and elsewhere. Their contribution is very gratefully acknowledged below. In addition, there are one or two people in particular I would like to thank for contributing to this and previous editions.
From the first and second editions From Pearson Education, I would like to thank (in chronological order), Christina Wipf-Perry who originally suggested the idea of a European adaptation and who has continued to take an interest in this blossoming pedagogy; Tim Pitts, for his unfailing philosophical outlook; Sue Phillips, development editor for the first edition; Liz Tarrant, production editor for the first edition; Jane Powell, who commissioned the first set of research updates for the website; Matthew Smith, an author’s editor; and John Yates, the very tall and charming publisher who helped to launch the first edition. Finally, I would like to thank my current editors and publishers: Ruth Haggerty, Louise Lakey, Karen Mclaren and the incomparable Morten Fuglevand. The second edition was written as Fame Academy reached its denouement. I would like to thank the inmates, especially Ainslie and David, for many hours of terpsichorean entertainment. I would like to thank for the following colleagues who either reviewed draft manuscripts or chapters or assisted in the completion of the book in many other invaluable ways.
From the third edition Thanks, as ever, go to the indomitable Morten Fuglevand who was the guiding hand in this, and other, projects. His influence was enormous. Thanks, too, to Janey Webb for carrying on the Psychology torch, getting the third edition into shape and for assorted treats; Sarah Wild (for all the sterling help with figure queries); Stephen Jeffrey and Nada Jolic (for all the help with MyLab); Robert Chaundy and Jonathan Price for the punctillious copy-editing and proofing; Sarah Busby, Geoff Chatterton, Georgina Clark-Mazo, Nicola Shortt, Alun Swift, Maggie Wells, and the UK and AU marketing teams for all their hard work.
Thanks to the following for all their feedback and advice on the first, second and third editions. Dave Alcock Bruce Arnow Jane Barnet John H.W. Barrett Sarah Beck Joe Boden Glynis Breakwell Vicki Bruce Brian Brunswick Nicola Brunswick Andrew Calder David Carey Julia Cogan Gillian Cohen Martin Conway Neil Cooper Mats Danielsson Alyson Davis Sergia Della Sala Jan Deregowski Paul Emmelkamp Ann Erling Anthony Esgate Nigel Foreman Adrian Furnham Peter Garrard Ken Gilhooly Nitin Gogtay Caroline Green Ruth Green Sheila Hale Peter Halligan Usneeral B. Hamaker Trevor Harley Ronald Henss Kenneth Hugdahl Dai Jones Gail Kinman Paul Kinnear Winek Koisor
University of Bristol Stanford University Middlesex University University of Bristol University of Birmingham University of Plymouth University of Surrey Edinburgh University Middlesex University University of Cambridge University of Aberdeen Open University University of Durham University of East Anglia Lulea University of Technology Surrey University University of Edinburgh University of Aberdeen Amsterdam University Gothenburg University University of Westminster Middlesex University University College London Institute of Cognitive Neuroscience, UCL Brunel University Child Psychiatry Branch, NIMH University of Aberdeen Staffordshire University University of Cardiff University of Amsterdam University of Dundee University of Saarland University of Bergen University of Glamorgan University of Bedfordshire University of Aberdeen Pearson Education
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ACKNOWLEDGEMENTS
Virginia Lam Robert Logie Monicque M. Lorist Geoff Lowe Bjorn Lyxell Neil MaCrae Caroline Mansfield MarkMcDaniel Maggie McGonigle Aidan Moran Peter Morris David Moxon Tom Nugent Rory O’Connor Michael Oddy Adrian Parker Andy Peart John Pickering Arne Poulsen Jan Pryor Sandra Read Andries F. Sanders Tony Shelton Dean Keith Simonton Michele Surbey Frode Svartdal Jaqui Taylor Kevin Thomas Jimmie Thomson Zazie Todd Andy Tolmie Margit Torneus Andy Tramo Erik Wastlund Claire Wells Brian Young Rob Bell
University of East London University of Aberdeen University of Groningen, The Netherlands University of Hull Linkoping University University of Bristol Oxford Brookes University University of New Mexico University of Edinburgh University College Dublin University of Lancaster Peterborough Regional College Child Psychiatry Branch, NIMH University of Strathclyde Brain Injury Rehabilitation Trust Gothenburg University Blackwell University of Warwick University of Roskilde Wellington University University of Bedfordshire Vrije University Liverpool John Moores University University of California, Davis James Cook University University of Tromsø Bournemouth University Trinity College Dublin University of Strathclyde University of Strathclyde Umea University Harvard University Karlstad University University of Exeter Queen's University Belfast
From the fourth edition Thanks to all those who helped by offering feedback and suggestions for this fourth edition of Psychology. Mark Burgess Kate Eames Eddie Edgerton Ian Fairholm Nollaig Frost Kerry Greer Eilis Hennessy Philip A. Higham Fay Julal Maggie McGonigle Paddy O’Donnell Qazi Rahman Kevin Silber Ian Stewart John Turner Lorenzo Vigentini
Oxford Brookes University Coventry University University of the West of Scotland Bath University Middlesex University Mary Immaculate, Limerick University College Dublin University of Southampton Southampton Solent University Edinburgh University University of Glasgow Queen Mary University, London University of Derby Galway University University of East London Edinburgh University
Thanks also to the students from the University of Edinburgh and Southampton Solent University. And finally, I would like to thank Janey Webb for all her help, support and encouragement during the third transmogrification; Catherine Morissey, redoubtable production-editor-in-waiting, plus Tim Parker, Barbara Massam, Rose James, Jane Ashley, Leo Stanley and John Matthews for all their hard work on the fourth edition of the book and MyPsychLab. Also, thanks to Beth Rix and Robert Chaundy for their help on the Research and Study Guide for the third edition; all of the reps at Pearson for their indefatigable drive and tenacity; Dame Marjorie Scardino, for the coffee, the chat, and the honour of discussing the project with her; the staff at Coffee Bean and Costa in High Barnet for providing the space where the bulk of the research for the fourth edition was written up and the first draft revised; and Niki for her ‘how are yous?’, her love of leteeoos, and her patience.
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Publisher’s acknowledgements
We are grateful to the following for permission to reproduce copyright material:
Figures Figure 1.1 from Psychology’s status as a scientific discipline: its empirical placement within an implicit hierarchy of the sciences, Review of General Psychology, 8 (1), p. 65, Figure 2 (Simonton, D.K. 2004); Figure 1.2a from Foltveld, P. The psychological profession in Denmark. in Schorr, A. and Saari, S. (eds) Psychology in Europe., ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern; Figure 1.2b from Van Drunen, P. Professional psychology in the Netherlands: history and recent trends. In Schorr, A. and Saari, S. (eds) Psychology in Europe., ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern; Figure 1.3 from Montin, S. The public image of psychologists in Finland. Reproduced with permission from Psychology in Europe by Schorr, A. and Saari, S. (eds), ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern.; Figure 1.4 Stock Montage Inc.; Figure 1.5 by permission of The McGraw-Hill Companies; Figure 1.6a from The return of Phineas Gage: clues about the brain from a famous patient, Science, 264, pp. 1102–1105 (Damasio, H., Grabowski, T., Frank, R., Galaburda, A.M. and Damasio, A.R. 1994), Department of Neurology and Image Analysis Facility, University of Iowa; Figure 1.7 from Explicit and implicit processing of words and pseudowords by adult developmental dyslexics: A search for Wernicke’s Wortschatz?, Brain, 122 (Brunswick, N., McCory, E., Price, C., Frith, C. and Frith, U. 1999); Figure 3.1 from Public acceptance of evolution in 34 countries, Science, 313, p. 765 (Miller, J.D., Scott, E. and Okamoto, S. 11 August 2006), Reprinted with permission from AAAS; Figure 3.4 from Fig. 9.1, p. 241 from MOLECULAR BIOLOGY OF THE GENE, 4th ed. by James D. Watson, Nancy H. Hopkins, Jeffrey W. Roberts, Joan Argetsinger Steitz, and Alan M. Weiner. Copyright (c) 1987 by the Benjamin/Cummings Publishing Company, Inc. Reprinted by permission of Pearson Education, Inc.; Figure 3.5 CNRI/Science Photo Library Ltd.; Unnumbered figure on page 90 Science Photo Library Ltd: Jacopin; Figure 3.8 Corbis: Outline; Figure 3.10 from Durante et al, Personality and Social Psychology Bulletin, 34(11), pp. 1451–1460, Changes in women’s choice of dress across the ovulatory cycle: Naturalistic and laboratory task-based evidence (2008) (c) 2008, Sage Publications. Reprinted by permission of Sage Publications; Figure 3.11 from Patterns and universals of mate poaching across
53 nations: the effects of sex, culture and personality on romantically attracting another person’s partner, Journal of Personality and Social Psychology, 86(4), figure 2 pp. 560–584 (Schmitt, D.P. 2004), reprinted with permission of American Psychological Association and David P. Schmitt; Figure 4.2 Professor Peter Cull/Science Photo Library Ltd.; Figure 4.3 Harvard Medical School/Betty G. Martindale; Figure 4.16(a) BSIP, Astier/Science Photo Library Ltd., (b) Abby Johnston: John Reardon; Figure 4.17 from Coping with severe memory impairment, Neuropsychological Rehabilitation, 14(5), pp. 481–94 (Oddy, M. and Cogan, J. 2004), Psychology Press, reprinted by permission of the publisher (Taylor & Francis Group, http://www.informaworld.com); Figure 4.18 (a) University of Florida: Arturo Sinclair, (b) Landov Media: David Kamerman/The Boston Globe; Figure 4.20 Daniel Sambraus/Science Photo Library Ltd.; Figure 4.21a from Imaging cognition II: an empirical review of 275 PET and fMRI studies, Journal of Cognitive Neuroscience, 12(1), pp. 1–47 (Cabeza, R. and Nyberg, L. 2000), reprinted by permission of the authors; Figure 4.21b from Anjan Chatterjee, Commentary: A madness to the methods of cognitive neuroscience?, Journal of Cognitive Neuroscience, 17:6 (June, 2005), figure 1, pp. 847-9 (2005) (c) 2005 by the Massachusetts Institute of Technology; Figure 4.22 (a) Hank Morgan/Rainbow, (b) Dr J. McA. Jones, Good Samaritan Hospital, Portland, Oregon, USA.; Figure 4.23 Corbis/Owen Franken; Figure 4.24 Scott Camazine/Photo Researchers, Inc; Figure 4.25 Pearson Education/Prentice Hall; Figure 4.26 Reprinted with permission from Elsevier: Reprinted from NeuroImage, Vol. 45, Issue 3, B.A. Parris, G. Kuhn, G.A. Mizen, A.Benattayallah and T.L. Hodgson, Imaging the Impossible: An fMRI study of impossible causal relationships in magic tricks, 1033-39, copyright 2009; Figure 4.27 Reprinted with permission from Elsevier: Reprinted from NeuroImage, vol. 40, issue 3, S.a. Spence, C. Kaylor-Hughes, T.F.D. Farrow and I.D. Wilkinson, Speaking Secrets and Lies: The contribution of ventrolateral prefrontal cortex to vocal deception, pages 1411-18, copyright 2008; Figure 4.28 University of Durham/Simon Fraser/Science Photo Library Ltd.; Figures 4.30a, 4.30b from Physiology of Behavior, 6th ed., Ally & Bacon (Carlson, N.R. 1998) p. 235 (c) Allyn & Bacon. Reproduced with permission; Figure 4.31 (b) Tissuepix/Science Photo Library Ltd.; Figure 4.36 from Pinel, BIOPSYCHOLOGY, Fig. 4.36 © 2003, 2000, 1997 Allyn and Bacon Reproduced by permission of Pearson Education, Inc.; Figure 4.37 Science Photo Library Ltd.; Figure 4.41 from Mental health of teenagers who use cannabis, British Journal of Psychiatry, 150, pp. 216–221 (Rey, J.M., Sawyer, M.G., Raphael,
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B., Patton, G.C. and Lynskey, M. 2002), reprinted by permission of the Royal College of Psychiatrists; Figure 5.3 J. Silver/SuperStock; Figure 5.10 Richard Elliot/Stone/Getty; Figure 5.12 Courtesy of Douglas G. Mollerstuen, New England Medical Center; Figure 5.14 adapted from Proceedings of the Royal Society (London), Series B, 166, pp. 80–111 (Dowling, J.E. and Boycott, B.B. 1966), redrawn by permission of the Royal Society; Figure 5.16 from The disappearance of steady fixated visual test objects, Journal of the Optical Society of America, 43, pp. 495-501 (Riggs, L.A., Ratliff, F., Cornsweet, J.C. and Cornsweet, T.N. 1953); Figure 5.22 Courtesy of American Optical Corporation; Figure 5.23 Brash, S., Maranto, G., Murphy, W. and Walker, B. (1990) How Things Work: The brain. Virginia: Time-Life Books. © 1990 Time-Life Books; Figure 5.26a from Principles of Behavioral Neuroscience, McGraw-Hill (Beatty, J. 1995) reprinted with permission of Jackson Beatty; Figures 5.28, 5.30, 5.31, 5.32 (b), 5.39 and 5.40 From GOLDSTEIN. Sensation and Peception, 7E. © 2007 Wadsworth, a part of Cengage learning, Inc. Reproduced by permission. www.cengage.com/ permissions; Figure 5.29 from Cognitive Psychology, Houghton Mifflin (Payne, D.G. and Wenger, M. 1998) p. 75 (c) 1998 Houghton Mifflin Company. Used with permission; Figure 5.33 from Pinel, BIOPSYCHOLOGY BEYOND THE BRAIN & BEHAVIOR CD, fig. 5.33 (c) 2003, 2000, 1997 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 5.35 Whitfield, P. and Stoddart, M. Pathways of Perception. New York: Torstar Books; Figure 5.36 Reprinted by permission from MacMillan Publishers Ltd: Nature Neuroscience vol.10. Nr.1, Jan 2007, copyright 2007 (r). Science Faction: Louie Psihoyos (l); Figure 5.38 Louis Psihoyos/Science Faction Images; Figure 6.9 from Cognitive Psychology, New York: Appleton-Century-Crofts (Neisser, U. 1967) reprinted with permission; Figure 6.13 adapted from Osherson, Daniel N., Stephen M. Kosslyn, and John Hollerbach, eds., An Invitation to Cognitive Science, Volume 2: Visual Cognition and Action, figure 2.4, adapted (c) 1990 Massachusetts Institute of Technology, by permission of the MIT Press; Figure 6.14 adapted from Osherson, Daniel N., Stephen M. Kosslyn, and John Hollerbach, eds., An Invitation to Cognitive Science, Volume 2: Visual Cognition and Action, figure 2.9, adapted (c) Massachusetts Institute of Technology, by permission of the MIT Press; Figure 6.17 from The effects of contextual scenes on the identification of objects, Memory and Cognition, 3, pp. 519–23 (Palmer, S.E. 1975), reprinted by permission of the Psychonomic Society, Inc.; Figure 6.19 Reproduced with permission from © The British Psychological Society: Journal of Neuropsychology; Figure 6.20 Reprinted with permission from Elsevier: Reprinted from Acta Psychologica, vol. 130, issue 2, R. McBain, D. Norton and Y. Chen, Females excel at basic face perception, pages 168–173, copyright 2009; Figure 6.21 Reproduced with permission from © The British Psychological Society: British Psychological Society; Figure 6.22 from Matlin/Foley, SENSATION & PERCEPTION, fig. 6.22 (c) 1992. Reproduced by permission of Pearson Education, Inc.; Figure 6.24 from Texture and visual perception, Scientific American, 212, pp. 34–38 (Julesz, B. 1965), reprinted with permission of Dr. Bela Julesz; Figure 6.27 Powerstock/SuperStock; Figure 6.30 from
HABER, Psychology of Visual Perception, 1st ed. (c) 1973 Wadsworth, a part of Cengage Learning, Inc. reproduced by permission, www.cengage.com/permissions; Figure 6.38 from Matlin/Foley, SENSATION & PERCEPTION, FIG. 6.38 (c) 1992. Reproduced by permission of Pearson Education, Inc.; Figure 6.45 Pearson Education Inc.; Figure 6.46 Cengage: Thomson Learning; Figure 6.50 from Human Neuropsychology, 2nd edn, Pearson/Prentice Hall (Martin, G.N., 2006). Image kindly provided by Dr Olaf Blanke; Figure 6.51 Chatterjee, A.A. madness to the methods of cognitive neuroscience? Journal of Cognitive Neuroscience, 2005, 17, 6, 847–9, © by the Massachusetts Institute of Technology; Figure 6.52 Reprinted from The Lancet, 350, P. Halligan and J. Marshall, The Art of Visual Neglect, pp. 139–40, Copyright 1997, with permission from Elsevier; Figure 7.4 adapted from Hill, LEARNING: A SURVEY OF PSYCHOLOGICAL INTERPRETATIONS, fig. 7.4 (c) 2002, 1997, 1990 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 7.5 from Hill, LEARNING: A SURVEY OF PSYCHOLOGICAL INTERPRETATIONS, fig. 7.5 (c) 2002, 1997, 1990 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 7.6 from Improving spatial awareness in physically disabled children using virtual environments, Engineering Science and Education Journal, 8(5), pp. 196–200 (Wilson, P.N. et al. 1999), reprinted by permission of the Institute of Electrical Engineers; Figure 7.10 Powerstock/SuperStock; Figure 7.11 from Insight and problem solving (Dominowski, R.L. and Dallob, P.) in, The Nature of Insight (Sternberg, R. and Davidson, J. (eds) 1996), Reproduced with permission from MIT Press; Figure 8.4 adapted from Visual Spatial Working Memory, Psychology Press Limited (Logie, R. 1995) p. 127 (c) 1995. Reprinted by permission of Psychology Press Limited, Hove, UK and Professor Robert Logie; Figure 8.15 Schmolck, H., Buffalo, E.A. and Squire, L.R., ‘Memory distortions develop over time: recollections of the OJ Simpson trial verdict after 15 and 32 months’, Psychological Science, 2000, 11(1), 39–45, reprinted by permission of Blackwell Publishers Ltd.; Figure 8.21 Reprinted by permission from Macmillan Publishers Ltd: NATURE, Place navigation impaired in rats with hippocampal lesions, 182(297), pp. 681–683 (Morris, R.G.M. et al. 1982), Copyright 1982; Figures 8.22, 8.23 from Recalling routes around London: Activation of the right hippocampus in taxi drivers, Journal of Neuroscience, 17, p. 7103 (Maguire, E.A., Frackowiak, R.S.J. and Frith, C.D. 1997) (c) 1997 by the Society for Neuroscience; Figure 8.24 reprinted by permission of Oxford University Press: I.G Dobbins and A.D. Wagner, Domain-general and domain-sensitive prefrontal mechanisms for recollecting events and detecting novelty, Cerebral Cortex November 2005, 15, pages 1768–78; Figure 9.2 from Hameroff, Stuart, Alfred Kaszniak, and Alwyn Scott, eds., Toward a Science of Consciousness II: The Second Tucson Discussions and Debates, figure 18.1 (c) 1998 Massachusetts Institute of Technology, by permission of the MIT Press; Figure 9.5 Strayer, D.L. and Johnston, W.A., Driven to distraction: Dual-task studies of simulated driving and conversing on a cellular telephone. Psychological Science, 2001, 12 (6), 462–6, reprinted by permission of Blackwell
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Publishers Ltd.; Figure 9.7 figure provided by Daniel Simons: Reproduced with kind permission Perception 1999, vol. 28, pages 1059-74, Simons D.J., Chabris C.F., “Gorillas in our midst sustained inattentional blindness for dynamic events.”; Figure 9.8 adapted from Human Neuropsychology, 2nd ed., Pearson Education (Martin, G.N. 2006), reproduced with permission; Figure 9.9 from Why We Sleep: The Functions of Sleep in Humans and other Mammals, Oxford University Press (Horne, J.A. 1988) figure 1.1 p. 10, By permission of Oxford University Press; Figures 9.10, 9.12 from The Biology of Dreaming, courtesy of Charles C Thomas, Publisher, Ltd. Springfield, Illinois (Hartmann, E. 1967); Figure 9.11 from Hobson, J.A., Consciousness. New York: W.H. Freeman, 1999; Figure 10.1 from The future of language, Science, 303, figure 1 p. 1329 (Graddol, D. 27 February 2004), copyright (2004) AAAS, Reprinted with permission from AAAS; Figure 10.2 from The future of language, Science, 303, p. 1330 (Graddol, D. 27 February 2004), copyright (2004) AAAS, Reprinted with permission from AAAS; Figure 10.3 from Cognitive Psychology, first ed., Houghton Mifflin (Payne, D.G. and Wenger, M.J. 1998) (c) 1998 by Houghton Mifflin Company. Used with permission; Figure 10.4 from Campbell, Lyle, Historical Linguistics: An Introduction, figure 6.1, redrawn (c) 1999 Massachusetts Institute of Technology, by permission of the MIT Press; Figure 10.5 from Just/Carpenter, PSYCHOLOGY OF READING, fig. 10.5 (c) 1987 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 10.6 from An interactive activation model of context effects in letter perception: Part 1: An account of basic findings, Psychological Review, 88, pp. 375–407 (McClelland, J.L. and Rumelhart, D.E. 1981), reprinted with permission of The American Psychological Association and James L. McClelland; Figure 10.7 from Principles that are invoked in the acquisition of words, but not facts, Cognition, 77, B33-B43 (Waxman, S.R. and Booth, A.E. 2000) (c) 2000, with permission of Elsevier; Figure 10.8 © 1999 Cable News Network, LP, LPP, All rights reserved.; Figure 10.10 from Language deficits and genetic factors, Trends in Cognitive Sciences, 1(1), p. 7 (Gopnik, M. 1997) (c) 1997, with permission from Elsevier; Figure 10.11 from On genes, speech and language, New England Journal of Medicine, p. 1655 (Fischer, S.E. 20 October 2005), Copyright (c) 2005 Massachusetts Medical Society. All rights reserved; Figure 10.13 PNAS: copyright 2008 National Academy of Sciences, USA; Figure 10.14 from Sound and meaning: how native language affects reading strategies, Nature Neuroscience, 3(1), pp. 3-5 (Fiez, J. 2000), reprinted by permission of the author; Figure 11.1 from Technical Supplement for the Culture Fair Intelligence Test Scales 2 and 3, figure 1, p.7 Originally published by The Institute of Personality and Ability Testing, Inc., Champaign, IL, USA Currently published by Hogrefe Ltd., Oxford, UK (www.hogrefe.co.uk). copyright (c) 1973 (c) 2008, by Hogrefe Ltd. Reproduced with permission. All rights reserved; Figure 11.3 from Decomposing self-estimates of intelligence: Structure and sex differences across 12 nations, © British Journal of Psychology, Vol Number:100, figure 1, pp. 429–442 (von Stumm, S., Charmorro-Premuzic, T. and Furnham, A. 2009), Reproduced with permission of The British Psychological Society;
Figure 11.4 from The effects of sex and context on paper and pencil spatial task performance, Journal of General Psychology, vol. 116, pp. 133–139 (Kalichman, S.C. 1989), reprinted by permission of the publisher (Taylor & Francis, http://www.informaworld.com); Figure 11.5 from Frequency curve and percent curve from the Stanford-Binet Intelligence Scales, First-Fourth Editions (SB) by Various, 1916, 1937, 1960, 1972, 1986, Austin: PRO-ED. Product number: R13376, with permission from Pro-Ed Inc.; Figure 11.7 © Bob Daemmrich/The Image Works. Reproduced with permission.;Figure 11.8 from Rising mean IQ: cognitive demand of mathematics education for young children, population exposure to formal schooling, and the neurobiology of the prefrontal cortex, Intelligence, 33, figure 1, p. 94 (Blair, C., Gamson, D., Thorne, S. and Baker, D. 2005), with permission of Elsevier; Figure 11.9 Katherine K. Sulik; Figures 11.10, 11.11 from The genetics of cognitive abilities and disabilities, Scientific American, 278(5), pp. 40–7 (Plomin, R. and DeFries, J.C. 1998), reprinted by permission of Dr. Jennifer C. Christiansen; Figure 11.12 from Reprinted from Neurobiology of Aging, 30(4), T. A. Salthouse, When does age-related cognitive decline begin? figure 2, pp. 507–14, Copyright 2009, with permission from Elsevier; Figure 11.13 from Beatty, J. (1995). Principles of Behavioral Neuroscience. New York: Brown and Benchmark/William C. Brown Communications Inc., Reprinted with permission; Figure 11.14 (a) Alfred Pasieka/Science Photo Library; Figure 11.15 Reprinted with permission from Elsevier: Reprinted from NeuroImage, 45, issue 3, A.D. Leow, I. Yanovsky, N. Parikshak, X. Hua, S. Lee, et al., Alzheimer’s Disease Neuroimaging Initiative: A one year follow up study using tensorbased morphometry correlating degenerative rates, biomarkers and cognition, pages 645–55, copyright 2009; Figure 11.16 from Cognitive deficits in the early stages of Alzheimer’s disease, Current Directions in Psychological Science 17, 3, 198–202. (Storandt, M. 2008), Wiley-Blackwell, reproduced with permission; Figure 11.17 Reprinted with permission from Elsevier: Reprinted from NeuroImage, vol. 45, issue 1, G.C.Schwindt and S.E. Black, Functional imaging studies of episodic memory in Alzheimer’s disease: a quantitive meta-analysis, pages 181–91, copyright 2009; Figure 11.18 (a) by permission of Oxford University Press: Oxford University Press, (c) Corbis: Basso uls Sophie/CORBIS Sygma; Figure 11.19 from Solso, COGNITIVE PSYCHOLOGY, fig. 11.19 (1998) Reproduced by permission of Pearson Education, Inc.; Figure 11.23 from Pinel, BIOPSYCHOLOGY, fig. 11.23 (c) 2003, 2000, 1997 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 12.1 Neil Harding/Getty Images; Figure 12.3 from Berk, CHILD DEVELOPMENT, fig. 12.3 (c) 1997 Pearson Education, Inc. Reproduced by permission of Pearson Education, Inc.; Figure 12.4 Images courtesy of P. Ellen Grant, M.D.; Figure 12.5 from The development of the brain, Scientific American, 241, pp. 106–17 (Cowan, W.M. 1979), with permission of Nelson H. Prentiss; Figure 12.6 adapted from Pattern perception in early infancy (Salapateck, P.), Infant Perception: From Sensation to Cognition (Cohen, L.H. and Salapateck, P. (eds) 1975), Copyright 1975, with
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permission from Elsevier; Figure 12.9 from Reactions to responsive contingent stimulation in early infancy, Merrill-Palmer Quarterly, 18, pp. 219–227 (Watson, J.S. and Ramey, C.T. 1972); Figure 12.10 W.H. Freeman and Company; Figure 12.11 from Of Children: An introduction to child development, 4th ed., Wadsworth (Lefrancois, G.R. 1983) with permission of Guy Lefrancois; Figure 12.12 adapted from Development functions for speeds of cognitive processes, Journal of Experimental Child Psychology, 45 p. 361 (Krails, R. 1988), Copyright 1988, with permission from Elsevier; Figure 12.13 from Autism: cognitive deficit or cognitive style?, Trends in Cognitive Sciences, 3(6), pp. 216–22 (Happé, F. 1999), copyright 1999, with permission of Elsevier; Figure 12.14 from Why may girls persist in smoking?, Journal of Adolescence, 22, pp. 657-72 (Crisp, A. et al 1999), copyright 1999, with permission of Elsevier; Figure 12.15 from Up and down in middle age: monotonic and nonmonotonic changes in roles, status and personality, Journal of Personality and Social Psychology, 89(2), pp. 194–204, APA (Helson, R. and Soto, C.J. 2005), reprinted with permission; Figure 12.16 National Centre on Health Statistics; Figure 12.17 from Thoughts for today, British Medical Journal, 331, p. 1550, unnumbered figure (24-31 December 2005), reproduced with permission from the BMJ Publishing Group; Figure 13.4 from How sensory properties of foods affect human feeding behaviour, Psychology and Behaviour, 29, pp. 409–417 (Rolls, B.J., Rolls, E.T. and Rowe, E.A. 1982), © 1982, with permission of Elsevier and Rolls, B.J. and Rolls, E.T.; Figure 13.5 from Obesity: responding to the global epidemic, Journal of Consulting and Clinical Psychology, 70(3), pp. 510–525 (Wadden, T.A., Brownell, K.D. and Foster, G.D. 2002), with permission of American Psychological Association and Shape Up America! www.shapeup.org; Figure 13.6 from What predicts weight regain in a group of successful weight losers?, Journal of Consulting and Clinical Psychology, 67(2), pp. 177–185 (McGuire, T.M., Wing, R.R., Klem, W., Lang, M.L. and Hill, J.O. 1999), with permission of American Psychological Association; Figure 13.7 Photo courtesy of Dr J. Sholtis, The Rockefeller University. © 1995 Amgen, Inc.; Figure 13.8 Reprinted with permission from Elsevier from Physiology & Behavior, vol. 94, issue 1, Walter Kaye, Neurobiology of anorexia and bulmia nervosa, pages 121–35, copyright 2008; Figure 13.9 Reprinted by permission of Oxford University Press and Bruce Arnow; Figures 13.10, 13.11 Paul Ekman Group, LLC; Figure 13.12 Science Photo Library Ltd/CLAUS LUNAU / BONNIER PUBLICATIONS; Figure 13.13 Science Photo Library Ltd.; Figure 13.14 from The return of Phineas Gage: Clues about the brain from a famous patient, Science 246, pp. 1102–1105 (Damasio, H. Grabowski, T., Frank, R., Galaburda, A.M. and Damasio, A.R. 1994); Figure 13.15 The Orion Publishing Group Ltd: Reproduced from Emotions Revealed by Paul Ekman, Weidenfeld & Nicolson, London; Figure 13.16 adapted from The repertoire of nonverbal behavior: categories, origins, usage and coding, Semiotica, 1, pp. 49-68 (Ekman, P. and Friesen, W. 1969), with permission of Mouton de Gruyter and Dr. Paul Ekman; Figure 13.17 from Inhibiting and facilitating conditions of the human smile: a nonobtrusive test of facial
feedback hypothesis, Journal of Personality and Social Psychology, 54, pp. 768–777 (Strack, F. et al. 1988), with permission of Prof. Dr. Fritz Strack; Figure 14.2 from 16PF® Fifth Edition Administrator’s Manual. , Copyright © 1993 by the Institute for Personality and Ability Testing, Inc., Champaign, Illinois, USA. All rights reserved. Reproduced with permission . “16PF” is a registered trade mark of IPAT Inc. IPAT is a wholly owned susidiary of OPP Ltd.; Figure 14.3 from Eysenck, H.J., The Inequality of Man. London: Temple Smith, 1973; Figure 14.4 from Human Neuropsychology, 2nd ed., Pearson Education (Martin, G.N. 2006), reproduced with permission; Figure 16.2 from Baron/Byrne, SOCIAL PSYCHOLOGY: UNDERSTANDING HUMAN INTERACTION, fig. 16.2 (c) 2006 Allyn & Bacon. Reproduced by permission of Pearson Education, Inc.; Figure 17.1 from Tackling health inequalities: all agenda for action (Whitehead, M. 1995) in Tackling Inequalities in Health: An Agenda for Action (Benzenal et al. (ed)); Figure 17.2 WHO: World health statistics 2007, part 1, 10 statistical highlights in global public health p. 13. www.who.int/whosis/whostat2007/en/ index.html; Figure 17.3 from Annual cigarette consumption per person for 1998, or latest available data, http://www.who.int/ tobacco/statistics/tobacco_atlas/en/, by permission of the World Health Organization; Figure 17.4 from Smoke-free Areas, http://www.who.int/tobacco/statistics/tobacco_atlas/en/, by permission of the World Health Organization; Figure 17.5 from World Health Statistics 2007, 1st ed., World Health Organization (2007) p. 15; Figure 17.6 from Countries which now ban tobacco advertising, http://www.who.int/tobacco/statistics/ tobacco_atlas/en/, by permission of the World Health Organization; Figure 17.7 from Health warnings and legislation, http://www.who.int/tobacco/statistics/tobacco_atlas/en/, by permission of the World Health Organization; Figures 17.8a, 17.8b from IAS Fact Sheet: Alcohol Consumption and Harm in the UK and EU London: IAS Unnumbered figures, p. 3 and p. 4; Figures 17.9a, 17.9b from IAS Fact Sheet: Alcohol Consumption and Harm in the UK and EU London: IAS Unnumbered maps, p. 7 and p. 8; Figure 17.10a from Aids (HIV Disease) Age standardised mortality in males aged 0+64 (1994-6) - NUTS 2 p. 111, Atlas on Mortality in the European Union, Map 21.1 Publications Office for the European Union (c) European Communities (2002); Figure 17.10b from Aids (HIV Disease) Age standardised mortality in females aged 0+64 (1994-6) - NUTS 2 p. 112, Atlas on Mortality in the European Union, Map 21.2 Publications Office for the European Union (c) European Communities (2002); Figure 17.11 from Seyle, H., Stress without Distress, © Lippincott Williams & Wilkins 1974; Figure 17.14 Andrejs Liepins/Science Photo Library/Photo Researchers Inc.; Figure 17.15 Reprinted from The Lancet, 346, J. K. Kiecolt, P. T. Marucha, W.B. Malarkey, A. M. Mercado, and R. Glaser, Slowing of wound-healing by psychological stress, pp. 1194–96, Copyright 1995 , with permission from Elsevier; Figure 17.17 from Longitudinal study of procrastination, performance, stress and health: the costs and benefits of dawdling, Psychological Science, 8(6), pp. 454-8 (Tice, D.M. and Baumeister, R.F. 1997), reprinted by permission of
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Blackwell Publishing Ltd.; Figure 17.18 from The impact of work on the psychological health and well-being of older Americans, Annual Review of Gerontology and Geriatrics, 26, pp. 153–174 (James, J.B. and Spiro, A. 2007) (c) Springer Publishing Company, Reproduced with the permission of the Springer Publishing Company, LLC, New York, NY 10036; Figure 18.1 Loren McIntyre/Woodfin Camp & Associates, Inc.; Figure 18.2 © Bettman/Corbis; Figure 18.6 from Repeated exposure of flight phobics to flights in virtual reality, Behaviour Research and Therapy, 39, pp. 1033–50 (Muhlberger, A. et al.), copyright 2000, with permission from Elsevier; Figure 18.8 from Neuroimaging and neuropathological studies of depressions: Implications for the cognitive-emotional features of mood disorders, Current Opinion in Neurobiology, 11 (Drevets, W.C.), copyright 2001, with permission from Elsevier; Figure 18.9 WHO: SUPRE suicide prevention information leaflet “Live Your Life” available online page 2, www.who.int/mental_health/management/en/ SUPRE_flyer1.pdf;
Tables Table 1.2 from Psychological evidence in court, The Psychologist, pp. 213–17 (Gudjonsson, G.H. May 1996), © The British Psychological Society, by kind permission of Professor Gudjonsson; Table 1.5 adapted from Friedlmayer, S. and Rossier, E. Professional identity and public image of Austrian psychologists. Reproduced with permission from Psychology in Europe by Schorr, A. and Saari, S. (eds), ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern.; Table 1.6 adapted from The 100 most eminent psychologists of the twentieth century, Review of General Psychology, 6, pp. 139–52 (Hagbloom, S.J., Warnick, R., Warnick, J.E., Jones, V.K., Yarborough, G.L., Russell, R.M., Borecky, C.M., McGahhey, R., Powell, J.L., Beavers, J. and Monte, E. 2002), with permission of Steve Haggbloom; Table 2.1 from The Barnam effect I: Personnel managers’ reactions to their ‘personality analysis’, Complementary Therapies in Medicine, 2, pp. 1–4 (Furnham, A. 1994), copyright 1994, reprinted with permission from Elsevier; Table 2.3 Extract 1 from Emanuel A. Schegloff, “On an Actual Virtual Servo-Mechanism for Guessing Bad News: A Single Case Conjecture”, Social Problems, Vol. 35, No. 4, 442–457 © 1988, The Society for the Study of Social Problems Inc. Used by permission. All rights reserved.; Table 2.3 Extract 2 from On clinicians co-implicating recipients’ perspectives in the delivery of diagnostic news (Maynard, D. W. 1992) 337-8, in Drew, P. and Heritage, J. (eds). Talk at Work. Cambridge:Cambridge University Press., reproduced with permission; Table 3.1 from Concepts of Genetics Scott, Foresman and Company, 1986 2nd ed. (Klug, W.S. and Cummings, M.R. 1986) Table 7.4 p.161 (c) 1986 Scott Foresman and Company, Reprinted by permission of Pearson Education, Inc.; Table 3.2 adapted from The heritability of attitudes: a study of twins, Journal of Personality and Social Psychology 80(6), pp. 845-60 (Olson, J.M., Vernon, P.A., Harris, J.A. and Lang, K.L. 2001), reprinted with permission of American
Psychological Association and James M. Olson; Table 8.1 from Remembering, Cambridge University Press (Bartlett, F.C. 1932), reproduced with permission;Table 9.1 from Pharmacology Churchill Livingstone (Rang, H.P., Dale, M.M. and Ritter, J.M. 1995) with permission of Elsevier; Table 10.5 from Berko Gleason, DEVELOPMENT OF LANGUAGE (c) 1997.Reproduced by permission of Pearson Education, Inc.; Tables 10.6, 10.7 adapted from Psychology and Language: An Introduction to Psycholinguistics, Wadsworth (Clark, H.H. and Clark, E.V. 1977) reprinted by permission of H.H. Clark & E.V. Clark; Table 10.8 from SavageRumbaugh, E.S., Language acquisition in nonhuman species, Development Psychology, 1990, 23, 599–620. Copyright © 1990, this material is used by permission of John Wiley & Sons, Inc.; Table 10.9 from Human Neuropsychology, 2nd ed., Pearson Education (Martin, G.N. 2006), reproduced with permission; Table 10.12 from Timothy Justus, The cerebellum and English grammatical morphology: evidence from production, comprehension, and grammaticality judgements, Journal of Cognitive Neuroscience, 16:7 (September, 2004), pp. 1115-30 (c) 2004 by the Massachusetts Institute of Technology; Table 11.1 adapted from Multivariate Statistical Methods, McGraw-Hill (Morrison, D.F. 1967) reprinted with permission of Donald F. Morrison; Table 11.2 adapted from Organization of abilities and the development of intelligence, Psychological Review, 75, p. 249 (Horn, J.L. 1968) (c) 1968 by the American Psychological Association. Adapted by permission; Table 11.4 adapted from Sex difference in intelligence, American Psychologist, 52(10), pp. 1091–1102 (Halpern, D.F. 1997), adapted with permission from The American Psychological Association and Diane Halpern; Table 11.5 adapted from Scarr, S. in Intelligence, Heredity and Environments (Sternberg, R.J. and Grigorenko, E. 1997), Cambridge University Press; Table 11.6 from Extensional versus intuitive reasoning: conjunction fallacy in probability judgement, Psychological Review, 90(4), pp. 293–315 (Tversky, A. and Kahneman, D. 1983), reprinted with permission of American Psychological Association and Professor Daniel Kahneman; Table 11.7 from Verbal creativity, depression and alcoholism, British Journal of Psychiatry, 168, pp. 545–55 (Post, F. 1996), reproduced with permission of the Royal College of Psychiatrists;Table 12.2 from Berk, CHILD DEVELOPMENT, table 12.2 (c) 1997 Pearson Education, Inc. Reproduced by permission of Pearson Education, Inc.; Table 12.6 adapted from What is successful ageing and who should define it?, British Medical Journal, 331, pp. 1548–51 (Bowling, A. and Dieppe, P. 2005), reproduced with permission from the BMJ Publishing Group; Table 13.1 adapted from The distribution of basic emotions in everyday life: a state and trait perspective from experience sampling data, Journal of Research in Personality, 34, pp. 178–97 (Zelenski, J.M. and Larsen, R.J. 2000), © 2000, with permission of Elsevier; Table 13.3 adapted from ‘No longer Gage’: frontal lobe dysfunction and emotional changes, Journal of Consulting and Clinical Psychology, 60(3), pp. 349–59 (Stuss, D.T., Gow, C.A. and Hetherington, C.R. 1992), © American Psychological Association. Adapted with permission of American Psychological Association and Dr. Donald
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Stuss; Table 13.4 adapted from Face and voice expression identification in patients with emotional and behavioural changes following ventral frontal lobe damage, Neuropsychology, 34(4), pp. 247–61 (Hornak, J., Rolls, E.T. and Wade, D. 1996), © 1996, with permission of Elsevier; Table 14.1 adapted from Personality and Individual Differences: A Natural Science Approach New York: Plenum Press (Eysenck, H.J. and Eysenck, M.W. 1985), with kind permission from Springer Science and Business Media; Table 15.4 adapted from Specificity of the attitude as a determinant of attitude–behavior congruence, Journal of Personality and Social Psychology, 30, pp. 724–8 (Weigel, R., Vernon, D.T.A. and Tognacci, L.N. 1974), © American Psychological Association, reprinted with permission of American Psychological Association and Dr. Russell Weigel; Table 16.1 from Out of mind but back in sight: stereotypes on the rebound, Journal of Personality and Social Psychology, 67, pp. 808–71 (Macrae, C.N., Bodenhausen, G.V., Milne, A.B. and Jetten, J. 1994) (c) American Psychological Association, with permission of American Psychological Association and Professor Neil Macrae; Table 17.1 from No Smoking Day website, www.nosmokingday.org.uk; Table 18.4 from Drugs and the treatment of psychiatric disorders: psychosis and anxiety (Baldessarini, R.J.) in, Goodman and Gilman’s:The Pharmacological Basis of Therapeutics, 9th ed. (Hardman, J.G. and Limbird, L.E. (eds) 1996), New York: McGraw-Hill, reproduced with permission of The McGraw-Hill Companies; Table 18.7 adapted from Carson, ABNORMAL PSYCHOLOGY AND MODERN LIFE, Table 18.8 (c) 1996 Pearson Education, Inc. Reproduced by permission of Pearson Education, Inc.; Table 18.8 from Cleckley, H., The Mask of Sanity, pp. 337–8. St. Louis: C.V. Mosby,1976; Table 18.9 from Drugs and the treatment of psychiatric disorders: psychosis and anxiety (Baldessarini, R.J.) in, Goodman and Gilman’s: The Pharmacological Basis of Therapeutics 9th ed. (Hardman, J.G. and Limbird, L.E. (eds) 1996), New York: McGrawHill, reproduced with permission of The McGraw-Hill Companies
Text Extract on page 47 from All in the Mind: The Essence of the Mind, Whurr (Furnham, A. 1996) pp. 83-84 (c) John Wiley & Sons Limited. Reproduced with permission; Article on page 75 from Science finds the secret of a hot kiss, The Sunday Times 8 February 2009, reproduced with permission; Article on page 113 from Found: the brain’s centre of vision, The Sunday Times 5 April 2009 (Leake, J.), Reproduced with permission; Article on page 167 from You really can smell fear, say scientists, The Guardian, 4 December 2008 (Randeson, J.), Copyright Guardian News & Media Ltd 2008; Extract on page 213 from Bruce, V. (1998). Fleeting images of shade, The Psychologist, 11, p. 331–337 For full article, see www.bps.org.uk/fios; Extract on page 257 adapted from Behavior Principles in Everyday Life, 3rd ed., Prentice Hall (Baldwin, John. D. and Baldwin, Janice. I. 1998) (c) 1998. Adapted by permission of Pearson Education, Inc., Upper Saddle River, NJ; Extract on page 291 from Forever Today by Deborah Wearing, published by Doubleday. Reprinted by permission of The Random
House Group Ltd.; Article on page 337 from Court told of sleep deprivation clue in Selby train case, The Guardian, 30 November 2001, Copyright Guardian News & Media Ltd 2001; Article on page 431 from Lessons from a tragedy, The Sunday Times Magazine, 23 June 2005 (Cornwell, J.), Reproduced with permission; Article on page 493 from Police refute Bridgend suicides linkn, Times Online, 19 February 2008 (Hines, N.), Reproduced with permission; Article on page 553 from How happiness can be catching, The Guardian, 5 December 2008 (Boseley, S.), Copyright Guardian News & Media Ltd. 2008; Article on page 609 from Mapped out: Britain’s personality clusters, The Sunday Times, 14 April 2009 (Leake, J. and Brooks, H.), Reproduced with permission; Article on page 647 from ‘MI5’ fantasy conman faces life sentence for deception, Times Online, 23 June 2005 (Freeman, S.), Reproduced with permission; Article on page 727 from Which? Calls for ‘fat tax’ on unhealthy food, The Guardian, 11 March 2009 (Smithers, R.), Copyright Guardian News & Media Ltd 2008
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It appears to be an almost universal belief that anyone is competent to discuss psychological problems, whether he or she has taken the trouble to study the subject or not, and that while everybody’s opinion is of equal value, that of the professional psychologist must be excluded at all costs because he might spoil the fun by producing some facts which would completely upset the speculation and the wonderful dream castles so laboriously constructed by the layman. Source: Eysenck, 1957, p. 13.
CHAPTER 1
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Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activities on: Behaviourism • Little Albert • The Skinnerian learning process • Fixed-interval and Fixed-ratio scheduling • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 1
• Define psychology and trace the history of the discipline. • Be aware of the different methods psychologists use to study behaviour.
• Distinguish between the branches of psychology and describe them.
• Describe and understand historical developments in psychology such as structuralism, behaviourism and the cognitive revolution.
• Be aware of how psychology developed in Europe and across the world.
• Understand what is meant by the ‘common-sense’ approach to answering questions about psychology and outline its flaws.
QUESTIONS TO THINK ABOUT
• Before you read this chapter, think about your own definition of psychology. Once you have finished reading Chapter 1, see whether your view has changed.
• What types of behaviour do you think a psychologist studies?
• Are there any behaviours that a psychologist cannot or should not study?
• What do you think psychologists mean when they say they adopt the ‘scientific approach’?
• Should psychological research always be carried out to help people?
• Do you think that much of what we know from psychology is ‘common sense’? Why?
• Are some psychological phenomena universal, i.e. they appear across nations and cultures?
• Can psychologists use data from animal experiments to
• How does psychology differ from other disciplines, such
draw meaningful conclusions about human behaviour?
as biology, sociology and physics? Which discipline/subjects do you think it is closest to and why?
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What is psychology? If you asked this question of several people, you would probably receive several, very different answers. In fact, if you asked this question of several psychologists, you would still not receive complete agreement on the answer. Psychologists engage in research, teaching, counselling and psychotherapy; they advise industry and government about personnel matters, the design of products, advertising, marketing and legislation; they devise and administer tests of personality, achievement and ability. And yet psychology is a relatively new discipline; the first modern scientific psychology laboratory was established in 1878 and the first person ever to call himself a psychologist was still alive in 1920. In some European universities the discipline of psychology was known as ‘mental philosophy’ – not psychology – even as late as the beginning of the twentieth century. Psychologists study a wide variety of phenomena, including physiological processes within the nervous system, genetics, environmental events, personality characteristics, human development, mental abilities, health, and social interactions. Because of this diversity, it is rare for a person to be described simply as a psychologist; instead, a psychologist is defined by the sub-area in which they work. For example, an individual who measures and treats psychological disorders is called a clinical psychologist; one who studies child development is called a developmental psychologist; a person who explores the relationship between physiology and behaviour might call themselves a neuropsychologist (if they study the brain) or a biopsychologist/physiological psychologist/psychobiologist (if they study the brain and other bodily processes, such as heart rate). Modern psychology has so many branches that it is often impossible to demonstrate expertise in all of these areas. Consequently, and by necessity, psychologists have a highly detailed knowledge of sub-areas of the discipline and the most common are listed in Table 1.1 on p. 9.
Psychology defined Psychology is the scientific study of behaviour. The word ‘psychology’ comes from two Greek words, psukhe, meaning ‘breath’ or ‘soul’, and logos, meaning ‘word’ or ‘reason’. The modern meaning of psycho- is ‘mind’ and the modern meaning of -logy is ‘science’; thus, the word ‘psychology’ literally means ‘the science of the mind’. Early in the development of psychology, people conceived of the mind as an independent, free-floating spirit. Later, they described it as a characteristic of a functioning brain whose ultimate function was to control behaviour. Thus,
the focus turned from the mind, which cannot be directly observed, to behaviour, which can. And because the brain is the organ that both contains the mind and controls behaviour, psychology very soon incorporated the study of the brain. The study of physical events such as brain activity has made some psychologists question whether the word ‘mind’ has any meaning in the study of behaviour. One view holds that the ‘mind’ is a metaphor for what the brain does; because it is a metaphor it should not be treated as if it actually existed. In his famous book The Concept of Mind, the philosopher Gilbert Ryle describes this as the ‘ghost in the machine’ (Ryle, 1949). One might, for example, determine that the personality trait of extroversion exists and people will fall on different points along a dimension from very introvert to very extrovert. But does this mean that this trait really exists? Or is it a label used to make us understand a complex phenomenon in a simpler way? This is called the problem of reification in psychology: the assumption that an event or phenomenon is concrete and exists in substance because it is given a name. The approach adopted by modern psychology is scientific, that is, it adopts the principles and procedures of science to help answer the questions it asks. Psychologists adopt this approach because they believe that it is the most effective way of determining ‘truth’ and ‘falsity’; the scientific method, they argue, incorporates fewer biases and greater rigour than do other methods. Of course, not all approaches in psychology have this rigorous scientific leaning: early theories of personality, for example, did not rely on the scientific method (these are described in Chapter 14). Recent developments in the methodology of psychology have yielded methods that are not considered to be part of the scientific approach: qualitative approaches to human behaviour, for example, reviewed in next chapter. For the moment, however, consider the value of this approach in psychology. Imagine that you were allowed to answer any psychological question that you might wish to ask: what is the effect of linguistic deprivation on language development, say, or the effect of personality on the stability of romantic relationships? How would you set about answering such questions? What approach do you think would be the best? And how would you ensure that the outcome of your experiment is determined only by those factors you studied and not by any others? These are the types of problem that psychologists face when they design and conduct studies. Sometimes, the results of scientific studies are denounced as ‘common sense’: that they were so obvious as to be not worth the bother of setting up an experiment. The view, however, is generally ill-informed because, as you will discover throughout this book, psychological research frequently contradicts common-sense views. As the late, influential
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British psychologist Hans Eysenck noted in this chapter’s opening quote, most people believe that they are experts in human behaviour. And to some extent we are all lay scientists, of a kind, although generally unreliable ones.
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Psychological research, however, frequently contradicts people’s assumed expertise as the Controversies sectionbelow illustrates.
Cutting edge – How much of a science is psychology?
• the number of theories and laws mentioned in introductory textbooks (the higher the ratio of theory to law, the ‘softer’ – i.e. less scientific – the discipline); • publication rate (the more frequent, the more scientific the discipline); • the appearance of graphs in journal papers (the ‘harder’ the discipline, the greater the number of graphs); • the impact made by young researchers (the more scientific the discipline, the greater the agreement that a researcher’s contribution is significant); • how peers evaluated 60 of their colleagues in their own disciplines, and how often single papers are cited (referred to in research papers). Simonton also looked at other measures of scientific standing: ‘lecture disfluency’ (the number of pause words such as ‘uh, ‘er’ and ‘um’: these are more common in less formal, less structured and less factual disciplines); the extent to which
references in journal articles were recent; the age at which a person received the Nobel prize; and perceived difficulty of the discipline. Simonton combined these measures to provide a composite measure of scientific status. Based on the first set of indicators, Simonton found that the natural sciences were judged to be more ‘scientific’ than were the social sciences. Psychology fell right on the mean – at the junction between natural and social sciences, as Figure 1.1 shows. However, psychology’s score was much closer to biology than to sociology. The biggest gap in scores was found between psychology and sociology, suggesting that the discipline is closer to its natural science cousins than its social science acquaintances.
Composite score
Psychology is a young science and the discipline has tried hard to earn and demonstrate its scientific spurs. Chemistry, physics or biology seem to have no such problems: their history is testament to their status as a science. A new study, however, suggests that psychology is gaining ground. Simonton (2004) compared the scientific status of psychology with that of physics, chemistry, sociology and biology. He identified a number of characteristics that typified a general science including:
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Physics Chemistry
Biology
Psychology
Sociology
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Rank in hierarchy
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The stereotypical image of a psychologist (a) and a traditional scientist (b). Source: (a) Pelaez Inc./Corbis; (b) Tomas de Arno/Alamy Images.
Figure 1.1 According to Simonton’s study, psychology’s scientific status was more similar to that of biology than other disciplines traditionally associated with it, such as sociology. Source: D.K. Simonton, ‘Psychology’s status as a scientific discipline: its empirical placement within an implicit hierarchy of the sciences’, Review of General Psychology, 2004, 8, 1, p. 65 (Fig. 2).
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Cutting edge – Continued A gap also separated chemistry and biology, suggesting that the sciences might be grouped according to three clusters: the physical sciences (chemistry and physics), life sciences (biology and psychology) and social science (sociology). Simonton concludes with an interesting observation. He argues that psychology’s position in this hierarchy does not
really reflect its scientific approach but its subject matter: because the subject matter of psychology can be viewed as not directly controllable or manipulable it may be perceived erroneously, despite its adoption of the scientific method, as neither scientific fish nor fowl.
Controversies in Psychological Science – Is psychology common sense? The issue Take a look at the following questions on some familiar psychological topics. See how many you can answer correctly.
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1 Schizophrenics suffer from a split personality. Is this: (a) true most of the time activit ee (b) true some of the time (c) true none of the time, or yp sych (d) true only when the schizophrenic is undergoing psychotherapy? 2 Under hypnosis, a person will, if asked by a hypnotist: (a) recall past life events with a high degree of accuracy (b) perform physical feats of strength not possible out of hypnosis (c) do (a) and (b), or (d) do neither (a) nor (b)? 3 The learning principles applied to birds and fish also apply to: (a) humans (b) cockroaches (c) both (a) and (b), or (d) neither (a) nor (b)? 4 Are physically attractive people: (a) more likely to be stable than physically unattractive people (b) equal in psychological stability (c) likely to be less psychologically stable, or (d) likely to be much more unstable? How well do you think you did? In a study published in 1997, these four questions featured in the ten most difficult questions answered by first-year psychology undergraduates who completed a 38-item questionnaire about psychological knowledge (Martin et al., 1997). In fact, when the responses from first- and final-year psychology, engineering, sociology,
English and business studies students were analysed, no one group scored more than 50 per cent correct. Perhaps not surprisingly, psychologists did significantly better than the other students, with sociologists following close behind. Why should psychology (and other) students perform so badly on a test of psychological knowledge? The answer lies in the fact that the questionnaire was not really a test of psychological knowledge but of common-sense attitudes towards psychological research. Common-sense mistakes are those committed when a person chooses what they think is the obvious answer but this answer is incorrect. Some writers suggested that ‘a great many of psychology’s basic principles are self-evident’ (Houston, 1983), and that ‘much of what psychology textbooks purport to teach undergraduates about research findings in the area may already be known to them through common, informal experiences’ (Barnett, 1986). Houston reported that although introductory psychology students answered 15 out of 21 questions about ‘memory and learning’ correctly, a collection of 50 individuals found in a city park on a Friday afternoon scored an average of 16. The 21 December 2008 edition of The Sunday Times featured a fullpage article, boldly headed ‘University of the bleedin’ obvious’, in which the journalist bemoaned what he perceived to be the triviality of (mostly) behavioural research. ‘Why are we,’ asked the journalist or his sub-editor, ‘deluged with academic research “proving” things that we know already?’, citing a string of seemingly irritating, self-evident bons mots from various university departments. Is the common-sense view of psychological research, justified?
The evidence Not quite. Since the late 1970s, a number of studies have examined individuals’ false beliefs about psychology, and students’ beliefs in particular. Over 76 per cent of first-year psychology students thought the following statements were true: ‘Memory can be likened to a storage chest in the brain into which we deposit
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Controversies in Psychological Science – Continued material and from which we can withdraw later’, ‘Personality tests reveal your basic motives, including those you may not be aware of’, and ‘Blind people have unusually sensitive organs of touch’. This, despite the fact that course materials directly contradicted some of these statements (Vaughan, 1977). Furnham (1992, 1993) found that only half of such ‘common-sense’ questions were answered correctly by 250 prospective psychology students, and only 20 per cent of questions were answered correctly by half or more of a sample of 110 first-year psychology, fine arts, biochemistry and engineering students. In Martin et al.’s (1997) study, final-year students answered more questions correctly than did first-year students but there was no significant difference between firstand final-year psychology students. This suggests that misperceptions are slowly dispelled after students undergo the process of higher education and learning, but that studying specific disciplines does nothing to dispel these myths effectively. This is just one explanation. What, then, is ‘common’ about ‘common sense’? Some have likened common sense to fantastical thinking. This describes ways of reasoning about the world that violate known scientific principles (Woolley, 1997). For example, the beliefs that women can control breast cancer by positive thinking (Taylor, 1983), that walking under a ladder brings bad luck and that touching wood brings good luck (Blum and Blum, 1974) violate known physical laws, but people still believe in doing such things. People often draw erroneous conclusions about psychological knowledge because they rely on small sets of data, sometimes a very small set of data (such as a story in a newspaper or the behaviour of a friend). Take the relationship between a mental disorder such as schizophrenia and murders committed by schizophrenic patients, for example. Despite the small number of murders committed by schizophrenic patients, the few cases which do receive media attention suggest that people with schizophrenia are uncon-
Explaining behaviour The ultimate goals of research in psychology are to understand, predict and change human behaviour: to explain why people do what they do. Different kinds of psychologists are interested in different kinds of behaviour and different levels of explanation. Not all psychologists study humans; some conduct research using laboratory animals or study the behaviour of wild animals in their natural habitat. Research using animals has provided many insights into the factors that affect human behaviour, such as the effect of sensory deprivation on the development of the senses.
trollable murderers who should be put out of harm’s way (the role of the media in promoting psychology is returned to in the next chapter). As you will see from the chapter on abnormal psychology (Chapter 18) this thinking is blatantly perverse: the majority of schizophrenic individuals will not cause harm to others. It is an example of what social psychologists call the ‘under-utilisation of base rate information’ (Fiske and Taylor, 1991; you will find more about this in Chapters 11, 15 and 16). It means that individual, vivid, single or a small number of examples are taken to represent the behaviour of an entire group. The base rate information (the actual incidence of behaviour in such groups in general), however, contradicts these single, vivid examples but is either ignored or dismissed. A similar process may be operating when people misperceive some aspects of psychology. Psychologists have discovered that two determinants of fantastical thinking are lack of information and an inability to explain behaviour. It seems likely that these factors could underpin misperceptions about psychology.
Conclusion As you work through your psychology course and through this book, discovering new and sometimes complicated ways of analysing and understanding human behaviour, you will realise that many of the beliefs and perceptions you held about certain aspects of psychology are false or only half right. Of course, no science is truly infallible and there are different ways of approaching psychological problems (and perhaps, sometimes, some problems are insoluble or we have no good method of studying them satisfactorily). Psychology, however, attempts to adopt the best of scientific approaches to understanding potentially the most unmanageable of subject matter: behaviour. And, for those of you who were wondering, the answers to the questions at the start of the box are c, d, c and a.
How do psychologists ‘explain’ behaviour? First, they must describe it accurately and comprehensively. We must become familiar with the things that people (or other animals) do. We must learn how to categorise and measure behaviour so that we can be sure that different psychologists in different places are observing the same phenomena. Next, we must discover the causes of the behaviour we observe – those events responsible for its occurrence. If we can discover the events that caused the behaviour to occur, we have ‘explained’ it. Events that cause other events (including behaviour) to occur are called causal events or determinants.
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For example, one psychologist might be interested in visual perception and another might be interested in romantic attraction. Even when they are interested in the same behaviour, different psychologists might study different levels of analysis. Some look inside the organism in a literal sense, seeking physiological causes, such as the activity of nerve cells or the secretions of glands. Others look inside the organism in a metaphorical sense, explaining behaviour in terms of hypothetical mental states, such as anger, fear, curiosity or love. Still others look only for events in the environment (including things that other people do) that cause behaviours to occur.
Established and emerging fields of psychology ee
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Throughout this book you will encounter many types of psychologist and many types of psycholyp sych ogy. As you have already seen, very few individuals call themselves psychologists, rather they describe themselves by their specialism – cognitive psychologist, developmental psychologist, social psychologist, and so on. Before describing and defining each branch of psychology however, it is important to distinguish between three general terms: psychology, psychiatry and psychoanalysis. A psychologist normally holds a university degree in a behaviour-related discipline (such as psychology, zoology, cognitive science) and usually possesses a higher research degree (a Ph.D. or doctorate) if they are teaching or a researcher. Those not researching but working in applied settings such as hospitals or schools may have other, different qualifications that enable them to practise in those environments. Psychiatrists are physicians who have specialised in the causes and treatment of mental disorder. They are medically qualified (unlike psychologists, who nonetheless do study medical problems and undertake biological research) and have the ability to prescribe medication (which psychologists do not). Much of the work done by psychologists in psychiatric settings is similar to that of the psychiatrist, implementing psychological interventions for patients with mental illness. Psychoanalysts are specific types of counsellor who attempt to understand mental disorder by reference to the workings of the unconscious. There is no formal academic qualification necessary to become a psychoanalyst and, as the definition implies, they deal with a limited range of behaviour. Most research psychologists are employed by colleges or universities, by private organisations or by government. Research psychologists differ from one another in two principal ways: in the types of behaviour they investigate and in the causal events they analyse. That is, they explain different types of behaviour, and they explain them in
terms of different types of cause. For example, two psychologists might both be interested in memory, but they might attempt to explain memory in terms of different causal events – one may focus on physiological events (such as the activation of the brain during memory retrieval) whereas the other may focus on environmental events (such as the effect of noise level on task performance). Professional societies such as the American Psychological Association and the British Psychological Society have numerous subdivisions representing members with an interest in a specific aspect of psychology. This section outlines some of the major branches or subdivisions of psychology. A summary of these can be found in Table 1.1. Psychobiology/biological psychology is the study of the biological basis of behaviour (G. N. Martin, 2003). Other terms for the same branch include physiological psychology and biopsychology. It investigates the causal events in an organism’s physiology, especially in the nervous system and its interaction with glands that secrete hormones. Psychobiologists study almost all behavioural phenomena that can be observed in non-human animals, including learning, memory, sensory processes, emotional behaviour, motivation, sexual behaviour and sleep, using a variety of techniques described in Chapter 4. Psychophysiology is the measurement of people’s physiological reactions, such as heart rate, blood pressure, electrical resistance of the skin, muscle tension and electrical activity of the brain (Andreassi, 2001). These measurements provide an indication of a person’s degree of arousal or relaxation. Most psychophysiologists investigate phenomena such as sensory and perceptual responses, sleep, stress, thinking, reasoning and emotion. Neuropsychology and neuroscience examine the relationship between the brain and spinal cord, and behaviour (Martin, 2006). Neuropsychology helps to shed light on the role of these structures in movement, vision, hearing, tasting, sleeping, smelling and touching as well as emotion, thinking, language and object recognition and perception, and others. Neuropsychologists normally (but not always) study patients who have suffered injury to the brain – through accident or disease – which disrupts functions such as speech production or comprehension, object recognition, visual or auditory perception, and so on. Clinical neuropsychology involves the identification and treatment of problems arising from nervous system disorders and injuries. Clinical neuropsychologists typically work in a hospital and collaborate closely with neurologists (physicians who specialise in diseases of the nervous system), although some teach or work in private practice. Modern neuropsychology also relies on sophisticated brain imaging techniques such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) which allow researchers to monitor the activity of the brains of individuals while they perform some psycho-
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Table 1.1 The major branches of psychology Branch
Subject of study
Psychobiology/Biological psychology
Biological basis of behaviour
Psychophysiology
Psychophysiological responses such as heart rate, galvanic skin response and brain electrical activity
Neuropsychology
Relationship between brain activity/structure and function
Comparative psychology
Behaviour of species in terms of evolution and adaptation
Ethology
Animal behaviour in natural environments
Sociobiology
Social behaviour in terms of biological inheritance and evolution
Behaviour genetics
Degree of influence of genetics and environment on psychological factors
Cognitive psychology
Mental processes and complex behaviour
Cognitive neuroscience
Brain’s involvement in mental processes
Developmental psychology
Physical, cognitive, social and emotional development from birth to senescence
Social psychology
Individuals’ and groups’ behaviour
Individual differences
Temperament and characteristics of individuals and their effects on behaviour
Cross-cultural psychology
Impact of culture on behaviour
Cultural psychology
Variability of behaviour within cultures
Forensic and criminological psychology
Behaviour in the context of crime and the law
Clinical psychology
Causes and treatment of mental disorder and problems of adjustment
Health psychology
Impact of lifestyle and stress on health and illness
Educational psychology
Social, cognitive and emotional development of children in the context of schooling
Consumer psychology
Motivation, perception and cognition in consumers
Organisational or occupational psychology
Behaviour of groups and individuals in the workplace
Ergonomics
Ways in which humans and machines work together
Sport and exercise psychology
The effects of psychological variables on sport and exercise performance, and vice versa
logical task. This approach combines two approaches in psychology: neuroscience and cognitive psychology (see below). Because of this, the area of study is sometimes described as cognitive neuroscience (Gazzaniga, 1995) or behavioural neuroscience. A new development in this area has been the study of the psychobiological processes involved in social behaviour, a sub-branch called social neuroscience. Social neuroscientists examine the role of the brain in behaviours such as empathy, turn-taking, seeing things from another person’s point of view, social interaction, political outlook, and so on. We look at the work of cognitive/behavioural/social neuroscientists in more detail in Chapter 4 and throughout this book. Comparative psychology is the study of the behaviour of members of a variety of species in an attempt to explain behaviour in terms of evolutionary adaptation to the environment. Comparative psychologists study behavioural phenomena similar to those studied by physiological psychologists. They are more likely than most other psychologists to study inherited behavioural patterns, such as courting and mating, predation and aggression, defensive behaviours and parental behaviours.
Closely tied to comparative psychology is ethology, the study of the biological basis of behaviour in the context of the evolution of development and function. Ethologists usually make their observations based on studies of animal behaviour in natural conditions and investigate topics such as instinct, social and sexual behaviour and cooperation. A sub-discipline of ethology is sociobiology which attempts to explain social behaviour in terms of biological inheritance and evolution. Ethology and sociobiology are described in more detail in Chapter 3, as is evolutionary psychology (an approach which interprets behaviour in terms of evolution). Behaviour genetics is the branch of psychology that studies the role of genetics in behaviour (Plomin and DeFries, 1998). The genes we inherit from our parents include a blueprint for the construction of a human brain. Each blueprint is a little different, which means that no two brains are exactly alike. Therefore, no two people will act exactly alike, even in an identical situation. Behaviour geneticists study the role of genetics in behaviour by examining similarities in physical and behavioural characteristics of blood relatives, whose genes are more similar
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than those of unrelated individuals. They also perform breeding experiments with laboratory animals to see what aspects of behaviour can be transmitted to an animal’s offspring. Of course, genetic differences are only one of the causes of individual differences. People have different experiences, too, and these experiences will affect their behaviour. Behavioural geneticists study the degree to which genetics are responsible for specific behaviours such as cognitive ability. We examine the work of behavioural geneticists in Chapter 3 and evaluate the contribution of this research to the study of intelligence (in Chapter 11 (and to other topics, such as personality) and throughout the book). Cognitive psychology is the study of mental processes and complex behaviours such as perception, attention, learning, memory, concept formation and problemsolving (Eysenck and Keane, 1995). To cognitive psychologists, the events that cause behaviour consist of functions of the human brain that occur in response to environmental events. Their explanations involve characteristics of inferred mental processes, such as imagery, attention, and mechanisms of language. Most cognitive psychologists do not study physiological mechanisms, but recently some have begun collaborating with neurologists and other professionals who utilise neuroimaging. A branch of cognitive psychology involves the modelling of human function using computer simulation or ‘neural networks’; this is called cognitive science and we briefly
examine the contribution of such computer simulations to our understanding of behaviour in Chapters 7 and 10. Developmental psychology is the study of physical, cognitive, emotional and social development, especially of children (Berk, 2009) but, more broadly, of humans from foetus to death (these psychologists are sometimes called lifespan developmental psychologists). Some developmental psychologists study the effects of ageing on behaviour and the body (a field called gerontology). Most developmental psychologists restrict their study to a particular period of development, such as infancy, adolescence or old age. This field is described and illustrated in more detail in Chapter 12. The development of children’s language is described in Chapter 10, and the effects of ageing on cognitive performance are reviewed in Chapter 11. Social psychology is the study of the effects of people on people. Social psychologists explore phenomena such as self-perception and the perception of others, causeand-effect relations in human interactions, attitudes and opinions, interpersonal relationships, group dynamics, and emotional behaviours, including aggression and sexual attraction (Hogg and Vaughan, 2007). Chapters 15 and 16 explore these issues and themes in social psychology and the Psychology in Action section here describes some of the recent, counter-intuitive findings from studies of a behaviour that is perennially fascinating but which also has serious consequences: lying.
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Take a look at the following behaviours? Which do you think are characteristic of a person who is lying. Think about the reasons for your choices. Averting gaze Unnatural posture Posture change Scratching/touching parts of the body Playing with hair or objects Placing the hand over the mouth Placing the hand over the eyes
Which of these did you think predicted lying? According to a standard manual of police interviewing, these features are all characteristic of a liar (Inbau et al., 1986). A study of participants in 75 countries found that ‘averting gaze’ was described as the best tell-tale sign of lying (Global Deception Research Team, 2006). Unfortunately, despite the manual’s exhortations and the international guesswork, none of these behaviours is actually reliably associated with deception and several studies have shown that general law enforcement officers are usually as poor as the average undergraduate at detecting truth and fal-
sity. Research by psychologists such as Aldert Vrij, for example, has highlighted how bad people are at detecting whether someone is telling the truth or is lying (Vrij, 2000, 2004b). However, it has also identified behaviours which are reliably associated with lying and suggests that the best way of detecting deception is to do so indirectly. Studies of police officers’ and students’ ability to detect deception, all report detection rates of between 40 and 60 per cent – a result no better than we would expect by chance (Vrij and Mann, 2001; Vrij, 2000; DePaulo and Pfeifer, 1986). Police officers and people who operate polygraphs – the so-called lie detector which measures skin conductance responses – generally do no better than students (Ekman and O’Sullivan, 1991). The exception to this generally ignominious performance seems to be Secret Service agents – police officers specifically trained to be sensitive to behaviour during interviewing, and criminals (Ekman et al., 1999). These groups tend to perform better than students and general law enforcement officers. Perhaps the best detectors of dissembling would be those who routinely lie in order to get out of trouble. Researchers from the University of Goteborg, Sweden (Hartwig et al., 2004) found that criminals were significantly better than students at
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Psychology in action – Continued
These are images of former American President Bill Clinton, British novelist Jeffrey Archer and former American President Richard Nixon. What features might have revealed that they were lying? Clinton claimed not to have had sexual relations with his intern, Monica Lewinsky, Jeffrey Archer was convicted of perjury, and Richard Nixon authorised but denied the tapping of 17 government officials’ and reporters’ telephones and those of opponents at the Democratic National Committee headquarters at the Watergate apartments. Source: PA Photos.
detecting liars. However, this finding was coloured by another – the criminals also detected fewer truth-tellers. The lie bias – that criminals are more likely to judge that someone is lying than telling the truth – might stem from the fact that criminals are naturally suspicious (because they are used to being lied to, whether in prison or in the context of their relationships with others) and because they themselves are practised liars (and, therefore, expect the worst of others). In another study, adult male offenders from a medium security Canadian prison and a group of undergraduates were asked to recall four emotional events from their lives (Porter et al., 2008) but lie about two of them. The researchers measured the number of illustrators (the use of hands to signify something), self-manipulations (touching/scratching the hand, head or body), frequency of head movement and number of smiles and laughs. Verbal indicators were number of words spoken per minute, filled pauses (‘umms’ and ‘ahs’), self-references and pauses longer than two seconds. Illustrators were higher when lying than not telling the truth in both groups. Offenders, however, used more self-manipulations when lying compared with non-offenders, a finding that seems to contradict previous studies. The authors suggest that this may be due to the specific context in which experiments take place, the type of lie, motivation, the consequences of the lie, and so on. The offenders also smiled less than the students when lying about emotional events. Of course, deception studies are fairly artificial: they usually involve participants watching a videotape of a person, and basing their judgement about the person’s truthfulness on
these data. Interviewing suspects, the police would argue, gives you much more information on which to base a judgement. Sadly, research does not support this view. Studies have shown that observers of an interview are better at discriminating between truth-tellers and liars than are the interviewers themselves (Buller et al., 1991; Granhag and Stromwall, 2001). The interviewers also showed evidence of truth bias – the tendency to declare that someone was saying the truth when they were not. People tend to focus on different behavioural cues when deciding on whether a person is telling the truth or lying, with people relying on verbal cues when judging the truthfulness of a story and on non-verbal cues when the story is deceptive (Anderson et al., 1999). What, therefore, signals that lying is taking place? Two of the most fairly reliable indicators appear to be a high-pitched voice and a decrease in hand movements. People are also better at identifying deception accurately if they are asked about it indirectly. For example, people are less accurate when asked, ‘Is this person lying?’ than when asked ‘Does the person x sincerely like the person y?’ (Vrij, 2001). When people are questioned indirectly they tend to focus on those behavioural cues that have been found to predict deception, such as decreased hand movement, rather than those that do not (Vrij, 2001). New research on lying is presenting us with some counterintuitive and challenging findings about psychology and human behaviour. Often as you saw in the Controversies in Psychological Science section earlier, these studies contradict ‘received wisdom’ and ‘common sense’.
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Individual differences is an area of psychology which examines individual differences in temperament and patterns of behaviour. The primary focus of individual differences research is on how large groups can be further subdivided into more meaningful groups. For example, instead of examining a group’s response to the effect of mild alcohol intake on task performance, a psychologist might decide to examine differences between men and women or people who are extraverted or introverted. Some examples of individual differences studied by psychologists include personality, intelligence, hand preference, sex and age. (The Cutting Edge section below looks at the role of personality in a behaviour that some have associated with mental ill-health: celebrity worship.) Cross-cultural psychology is the study of the impact of culture on behaviour (Segall et al., 1998). The ancestors of people of different racial and ethnic groups lived in different environments which presented them with different problems and opportunities for solving those problems. Different cultures have, therefore, developed different strategies for adapting to their environments. These strategies show themselves in laws, customs, myths, religious beliefs and ethical principles as well as in thinking, health beliefs and approaches to problem-solving. In each chapter of the book, you’ll find a section entitled, ‘. . . An international perspective’. This takes a topic in psychology and examines how it is has been studied cross-culturally, e.g. Are personality traits universal?, Is the recognition of emotion culture-specific?, Do culturespecific mental illnesses exist?, and so on. But throughout every chapter, you will discover how studies from research laboratories and centres across the world have contributed to our understanding of behaviour. A similar – but different – term, cultural psychology, has been used to describe the study of variations within cultures (not necessarily across cultures). The assumption in cultural psychology is that cultures, and their processes and contents, are variable and not universal (Miller, 1997). Forensic and criminological psychology applies psychological knowledge to the understanding, prediction and nature of crime and behaviour related to crime. There is a distinction between criminological and forensic psychology. Forensic psychologists can be commissioned by courts to prepare reports on the fitness of a defendant to stand trial, on the general psychological state of the defendant, on aspects of psychological research (such as post-traumatic stress disorders), on the behaviour of children involved in custody disputes and so on. Criminological psychology refers to the application of psychological principles to the criminal justice system (Blackburn, 1996). The terms, however, are often used interchangeably. One example of the way in which criminological psychologists can apply their research to crime is in the study of eyewitness testimony. Eyewitness testi-
mony is a highly unreliable source of information and psychologists have helped show how flawed this method of memory retrieval is and have suggested alternative methods of prompting witnesses’ memory of crime. We examine some of these methods in Chapter 8. The Psychology in Action section below also shows you some of the ways in which the work of psychologists has been useful to the criminal justice system, either by improving police detection techniques or by advising on the reliability of testimony. Many psychologists’ work can help to solve or understand pressing human problems such as drug and alcohol abuse, stress, susceptibility to illness, mental disorder, developmental disorders, work inefficiency, witness memory, eyewitness testimony, crowd control and so on. Clinical psychology ‘aims to reduce psychological distress and to enhance and promote psychological well-being by the systematic application of knowledge derived from psychological theory and data’ (BPS Division of Clinical Psychology, 2001). It is an applied branch of psychology because clinical psychologists do not work in the laboratory under well-controlled experimental conditions but out in the field, applying the knowledge gained from practice and research. Most clinical psychologists are specially trained practitioners who attempt to assess and treat people’s psychological problems. The remainder represent scientists who investigate a wide variety of causal events, including genetic factors, physiological factors and environmental factors such as parental upbringing, interactions with siblings and other social stimuli. Clinical psychologists can work in private practice (on their own or as part of a joint practice), in hospitals and mental health clinics, as part of government services, in work organisations, and sometimes as lecturers in colleges and universities. Chapter 18 describes some of the problems seen by clinical psychologists. Perhaps two of the greatest bugbears for psychologists have been the misrepresentation of research and the inaccurate reporting of research, such as the portrayal of mental illness. A research team from the University of Auckland, New Zealand, for example, analysed a week’s worth of children’s programmes on two television stations to see how mental illness was portrayed (Wilson et al., 2000). Forty-six different programmes were analysed representing 128 different episodes: 60 per cent were made in the USA and over 80 per cent were cartoon animations. Characters were defined as mentally ill if they were referred to by other characters as having a mental illness. Of the 128 episodes, over 45 per cent contained reference to mental illness. Most of these programmes were cartoons. The most common terms for mental illness were ‘crazy’, ‘mad’ and ‘losing your mind’, although ‘mad’ and ‘crazy’ were interchangeably used to mean ‘angry’. Other terms included ‘driven bananas’, ‘wacko’, ‘nuts’, ‘loony’,
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Cutting edge – I’m your biggest fan… What makes a celebrity worshipper worship? Shakespeare, in his day, probably had fans whose responses were a little overenthusiastic, but the explosion of media available in the twenty-first century means that people can now gorge themselves on as much information about their favourite celebrities as they want. According to research, fans (or ‘celebrity worshippers’) tend to be adolescents or young adults and enjoy ‘game-playing’ in romantic relationships. They appear to be no more or less shy or lonely than is normal but their degree of worship has been associated with psychological disorder. Some fans can cross the conventional line between worshipping at a distance and becoming overlyobsessed by their idol. Maltby, McCutcheon and their colleagues have described celebrity worship as having three components (Maltby et al., 2001; McCutcheon et al., 2002). Low levels of worship are characterised as having entertainment-social value (e.g. ‘My friends and I like to discuss what my favourite celebrity has done’). Intermediate levels are expressed in attitudes such as ‘I
consider my favourite celebrity to be my soul mate’ (intensepersonal value). Extreme levels, called borderline-pathological, are expressed in views such as ‘If I were lucky enough to meet my celebrity, and he/she asked me to do something illegal as a favour, I would probably do it’. Those expressing low levels of worship tend to be extravert (sociable, lively, active, etc.), those expressing intermediate levels tend to be neurotic (tense, moody, emotional), and those showing evidence of borderline-pathological attitudes express some of the traits seen in the psychoticism scale, such as impulsivity and antisocial behaviour (Maltby et al., 2003). In a study of the relationship between celebrity worship, personality and mental health, Maltby et al. (2004) found that in their sample of over 350 participants, 15 per cent were classified as expressing entertainment-social attitudes; 55 per cent expressed intense-personal attitudes; and 1 per cent expressed pathological attitudes. The researchers found that, as predicted in their previous study, the three levels of
(a)
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The two faces of celebrity. Mark Chapman was obsessed with J.D. Salinger’s The Catcher in the Rye and assassinated former Beatle John Lennon outside the Dakota Hotel in New York. In 2002, Japanese businessman Masahiko Shizawa was issued with a restraining order because he was ‘abnormally obsessed’ with Britney Spears.
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Source: (a) NYC PD/AFP/Getty Images; (b) Simon Frederick/Getty Images.
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Cutting edge – Continued worship were significantly correlated with personality type. Celebrity worshippers who followed their idols for entertainment or social reasons were extravert, sought information and support and were open in showing their emotions. Those who followed their idols for intense or personal reasons were neurotic. Those at the extreme end were more likely to use humour to cope with life, to use drink and drugs and to be non-religious.
‘cuckoo’ and ‘freak’. Mental illness was frequently portrayed as reflecting a loss of control. Characters at the receiving end of these epithets were routinely and invariably seen as negative, as objects of amusement or derision
Surprisingly, only one level of worship was associated with mental health problems. Those celebrity worshipping for intense-personal reasons had poorer general health (depression, anxiety and social dysfunction), expressed more negative affect (stress and low life satisfaction) and did not cope effectively with everyday life events. The researchers suggest that these problems may be underpinned by personality style (neuroticism) – one that reflects a disengagement from life.
or as objects of fear. The characters were either comical or villainous. You’ll see in the last chapter how psychologists have identified views such as these and proposed ways of changing them.
Psychology in action – Psychology in the witness box Recent years have seen a surge of interest in forensic or criminological psychology. Forensic psychology refers to the branch of psychology which involves the ‘collection, examination and presentation of evidence for judicial purposes’ (Haward, 1981; Blackburn, 1996). The British Psychological Society has its own division of criminological and legal psychology and a European Association for Psychology and Law has been established (Blackburn, 1996). Several popular accounts of the forensic psychologist’s work have been published (for example, Canter, 1994; Britton, 1997) and the day-to-day work of the profession has been fictionalised (not entirely accurately) in programmes and films such as Criminal Minds, Cracker, The Silence of the Lambs and Hannibal. The application of psychology to law, however, is a recent phenomenon. The first psychologist to give expert testimony in court was the German Albert Schrenk-Notzing in 1896. SchrenkNotzing became involved in the trial of a Munich man accused of murdering three women (Bartol and Bartol, 1987). His contribution helped the court to understand the concept of retroactive memory falsification – the confusion that arises between what witnesses say they saw and what actually happened. A little later, in the USA, the advice of Hugo Munsterberg, one of the pioneers of forensic psychology, was sought in two murder trials (Colman, 1995). His work on the reaction time between rifle shots was cited in the case relating to the assassination of John F. Kennedy (Haward, 1979; Colman, 1995). The psychologists most often consulted by lawyers are clinical and educational psychologists (Lloyd-Bostock, 1988;
Gudjonsson, 1996a). Prison psychologists might also be consulted to assess offenders and give supporting evidence in court; occupational psychologists might be called on in cases involving personal injury or discrimination; academic psychologists might be asked to advise on specialised areas of psychology, such as factors which could influence face identification (Lloyd-Bostock, 1988); clinical neuropsychologists might be asked to determine whether a defendant is malingering, i.e. feigning mental disorder or intellectual incompetence (Martin, 2006). See Table 1.2.
Table 1.2 The types of evidence provided by forensic psychologists Types of evidence provided
Interview with client Studying relevant documents Psychometric test results Interview with informants Behavioural assessment Other (e.g. reviewing audio/video material, conducting research reviews/psychophysiological measurements)
Percentage recorded 97 87 85 79 64
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Source: Based on the responses of 522 psychologists in the UK. Gudjonsson, G.H., Psychological evidence in court. The Psychologist, 1996, May, 213–17. © The British Psychological Society.
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Psychology in action – Continued At the trial stage of criminal proceedings, psychologists may assess an individual’s state of mind and determine whether the offence was intentional. Much of the empirical research in psychology could also be applied at this stage – especially research that can inform jurors’ understanding of behaviours such as witness memory and eyewitness identification (Loftus, 1986). In North America, and also in England and Wales in particular, the legal and police systems have taken steps to issue guidelines on, for example, eyewitness testimony and its reliability, such as the Memorandum of Good Practice on Video-recorded Interviews with Child Witnesses for Criminal Proceedings (1992) in the UK, and Eyewitness Evidence: A Guide for Law Enforcement (1999) in the US (Wells et al., 2000). One tool associated with criminological psychology, and which has given it some cinematic glamour, is offender profiling, a technique that dates back to the 1950s (Brown, 1998). The purpose of offender profiling is to present a composite description of a perpetrator, based on biographical and behavioural cues, that can lead to the apprehension of that perpetrator. It can also be used to narrow the focus of an investigation (by specifying the perpetrator’s age or sex, or where he/she lives) or to provide suggestions for interviewing suspects (McCann, 1992). By collating data and evaluating evidence, such techniques have led to the arrest of serious criminals, such as the British criminal, John Duffy, who murdered his victims near railways (Canter, 1989). However, even psychologists who have used – and pioneered – such techniques suggest caution in using this technique. The romantic, insightful detective who uses implicit learning to make his deductions dates back to Sherlock Holmes. In a review of offender profiling, a leading forensic psychologist, David Canter from the University of Liverpool, has argued that, ‘Much of what passes for “offender profiling” in practice and as reported in the factual and fictional media has no basis in empirical research’ (Canter, 2000). He criticises the ‘implicit reasoning’ approach, popularised by Conan Doyle in his Holmes stories, using an interesting illustration. Holmes’s approach involved using experience or logic to draw inferences about the criminal. In a real-life example cited by Canter, a victim had noticed that the assailant had short fingernails on the left hand and long ones on the right hand. Someone with information about guitar playing suggested that this was a characteristic of serious guitar players and the search was on for a guitarist. When the offender was eventually arrested, he was found to have no connection with guitars. He had asymmetrical fingernails because of his job as a tyre repairman.
‘I can never bring you to realise the importance of sleeves, the suggestiveness of thumbnails, or the great information that may hang from a bootlace,’ said the great Sherlock Holmes in A Case of Identity. Modern crime detection, however, would suggest that Holmes’s strategy would convict more innocent people than guilty. Source: 20th Century Fox/Kobal Collection Ltd.
Canter also describes a team of northern European profilers who mistakenly assumed that because a murdered woman’s face had been severely beaten, the offender knew his/her victim and was exacting some form of revenge (http://www.liv.ac.uk/ InvestigativePsychology/invpub.htm).The murdered woman was a teacher and attention was quickly focused on those pupils who may have been ignored or spurned by her. The murderer turned out to be a drug addict who killed the woman when she disturbed him burgling her house. Canter suggests adopting a more statistical approach to offender profiling: collecting bits of data so that consistencies between crimes can be highlighted. Although an individual crime will differ from crime to crime, there may be a consistent theme running through that series of crimes. Canter argues that this systematic, clinical approach is more likely to be successful in profiling offenders than is that of the lone detective working on hunches.
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Health psychology is the study of the ways in which behaviour and lifestyle can affect health and illness (Sarafino, 2002). For example, smoking is associated with a number of illnesses and is a strong risk factor for death. Health psychologists study what makes people initiate and maintain unhealthy behaviour and can help devise strategies to reduce it. Health psychologists are employed in a variety of settings including hospitals, government, universities and private practice. The work of health psychologists is described in Chapter 17. Educational psychology is another branch of applied psychology. Educational psychologists assess the behavioural problems of children at school and suggest ways in which these problems may be remedied. For example, the educational psychologist might identify a child’s early inability to read (dyslexia) and suggest a means by which this may be overcome through special training. The educational psychologist might also deal with all aspects relevant to a child’s schooling such as learning, social relations, assessment, disruptive behaviour, substance abuse, bullying and parental neglect. Consumer psychology is the study of the motivation, perception, learning, cognition and purchasing behaviour of individuals in the marketplace and their use of products once they reach the home. Some consumer psychologists take a marketer’s perspective, some take a consumer’s perspective, and some adopt a neutral perspective, especially if they work at a university.
Organisational or occupational psychology is one of the largest and oldest fields of applied psychology and involves the study of the ways in which individuals and groups perform and behave in the workplace (Huczynski and Buchanan, 2006). Early organisational psychologists concentrated on industrial work processes (such as the most efficient way to shovel coal), but organisational psychologists now spend more effort analysing modern plants and offices. They are involved in the administration and development of personality aptitude tests and can also be involved in stress management. Most are employed by large companies and organisations, but almost one-third are employed in universities. Ergonomics or human factors psychology focuses mainly on the ways in which people and machines work together (Shackel, 1996). They study machines ranging from cockpits to computers, from robots to MP3/4 players, from transportation vehicles for the disabled to telephones. If the machine is well designed, the task can be much easier, more enjoyable and safer. Ergonomists help designers and engineers to design better machines; because of this, the terms ergonomics and engineering psychology are sometimes used interchangeably (Stanton, 1996). Sport and exercise psychology applies psychological principles to the area of sport. It also involves the study of the effects of sport and exercise on mood, cognition, well-being and physiology. This area is examined in more detail in Chapter 17.
Psychology – An international perspective Behind almost all research endeavours in psychology is a common aim: to discover a psychological universal. According to Norenzayan and Heine (2005), psychological universals are ‘core mental attributes shared by humans everywhere’. That is, they are conclusions from psychological research that can be generalised across groups – ways of reasoning, thinking, making decisions, interpreting why people behave in the way that they do, recognising emotions and so on, are all examples of core mental attributes. A sound case for a psychological universal can be made if a phenomenon exists in a large variety of different cultures. However, as might be obvious to you, some differences may be more obvious in some groups than others – men and women, for example, the young and the old, the mentally ill and the mentally healthy, and so on. At this level of analysis, we cannot say that people in general behave in a particular way, but that a spe-
cific group of people behave in a particular way. Nowhere is this more relevant than when considering the role of culture in psychological studies. A variety of behaviours are absent or are limited in a variety of cultures and nations. Some recent research, for example, has highlighted significant differences between Western and Asian cultures in the types of autobiographical memory they recall, the parts of a landscape and photograph they focus on, and the way in which they draw and take a photograph. Table 1.3 summarises some of these differences. One approach to demonstrating a psychological universal is to examine a behaviour in three or more cultures, two of which are very different, with a third falling between them, and see how each differs from, or is similar to, the other. The best way, however, is to examine a variety of cultures, as Daly and Wilson (1988) did. Their research examined sex differences in the international rates of homicide and found that men were more
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Psychology – Continued Table 1.3 Behaviours which have been reported to vary across cultures, or which may be less evident in certain cultures. Unfamiliar terms are defined in the chapters referred to in brackets • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
Memory for and categorisation of focal colours Spatial reasoning (see Chapter 8) Autobiographical memory Perception of the environment Appreciation of art Some types of category-based inductive reasoning (see Chapter 11) Some perceptual illusions Some ways of approaching reasoning Aspects of numerical reasoning Risk preferences in decision-making (see Chapter 11) Self-concept (see Chapters 15 and 16) Similarity-attraction effect (see Chapters 15 and 16) Approach-avoidance motivation (see Chapter 13) The fundamental attribution error (see Chapters 15 and 16) Predilection for aggression Feelings of control High subjective well-being and positive affect Communication style Prevalence of major depression Prevalence of eating disorders (see Chapter 13) Mental illness (those that appear in some cultures but not others – see the Controversies in Psychological Science section in Chapter 18) Noun bias in language learning (see Chapter 10) Moral reasoning Prevalence of different attachment style (see Chapter 12) Disruptive behaviour in adolescence Personality types (see Chapter 14) Response bias (see Chapter 2) Recognition of emotion Body shape preference
Source: Adapted from Norenzayan and Heine (2005).
likely to kill men than women were to kill women. Debate then ensues as to why this universal should be (and that debate is often heated, as most in psychology are). A related approach is to examine the degree to which a psychological phenomenon is present –personality type is a good example of this. As Chapter 14 will show you, the dominant approach in personality views us as differing along five major personality dimensions. Cross-cultural research has highlighted (i) the universality of these five dimensions but also (ii) the differences or ‘variation’ which exist between and within cultures
within each dimension – so some cultures or states may express more or less of a personality type such as extraversion or conscientiousness, for example. In the book, examples of universals (and exceptions) are described in the sections: ‘. . . An international perspective’. These will help you put the findings you read about into some form of cultural or international context. They should also help demonstrate that although studies sometimes report findings as being absolute and generalisable to populations in general, sometimes these findings are not.
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Psychology: a European perspective Psychology is one of the most popular degree courses in Europe. In 2008, psychology was the third most popular UK University degree in terms of applications (70,295, pipped only by law and pre-clinical medicine, see Table 1.4). It is estimated that 1 in 850 people in the Netherlands has a degree in psychology (Van Drunen, 1995), and no course is more popular in Sweden (Persson, 1995). Modern psychology has its origins in Europe: the first psychological laboratory was established in Europe and some of the first designated university degrees in psychology were established there. Research in North America and Europe accounts for the majority of psychological studies published in the world (Eysenck, 2001) and there continues to be debate over whether these two fairly large ‘geographical’ areas adopt genuinely different approaches to the study of psychological processes (G. N. Martin, 2001). Psychology as a discipline occupies a different status in different European countries and each country has established its own degrees and societies at different times, for historical or political reasons. Almost all countries have a professional organisation which regulates the activity of psychologists or provides psychological training or licensing of psychologists. The first such association in Denmark was founded in 1929 (the Psychotechnical Institute in Copenhagen) and what we would now call educational psychology formed the basis of the professional training it provided: the job of the institute was to select apprentices for the printing trade (Foltveld, 1995). The Netherlands’ first psychological laboratory was founded in 1892 at Gröningen, Denmark’s in 1944 at the University of Copenhagen and Finland’s in 1921 by Eino Kaila at the University of Turku (Saari, 1995). Coincidentally, 1921 was also the year in which The Netherlands passed a Higher Education Act allowing philosophy students to specialise in psychology.
Table 1.4 The top ten degree subjects in the UK, as indexed by applications to study at university (2008) 1 2 3 4 5 6 7 8 9 10
Law Pre-clinical medicine Psychology English studies Management studies Nursing Teacher training Business/admin studies History Business studies
77,459 70,377 70,295 50,251 49,447 47,051 43,896 42,816 41,917 41,583
The British Psychological Society (BPS) was formed in 1901, with laboratories established at the University of Cambridge and University College London in 1897, closely followed by the establishment of laboratories in Aberdeen, Edinburgh and Glasgow (Lunt, 1995). Sweden’s professional association was founded in 1955 (Sveriges Psykologforbund), with the Netherlands’ predating that in 1938 (Nederlandsch Instituut van Practizeerende Psychologen, or NIPP). Portugal is one of the younger psychology nations – the first graduates in psychology left university in 1982 (Pereira, 1995). Because of the history of the country, psychology was not acknowledged as a university subject in Portugal until after the democratic revolution of 1974.
Psychological training and status of psychology in Europe The types of career that psychology graduates pursue are similar across most European countries. Figures 1.2(a) and (b) show you the employment destination of psychologists in Denmark and The Netherlands. You can see from these figures that most psychologists are employed in the public sector, with the majority of those working in the clinical, educational or organisational fields. Around 90 per cent of psychologists are employed in the public sector in Finland and 70 per cent of these work in health, clinical or social work-related areas (Saari, 1995). A similar pattern is seen in Sweden (Persson, 1995). Training for psychologists varies between countries and controversy surrounds the licensing or the legalisation of the profession. For example, psychologists in almost all countries wish for formal statutory regulation of the profession (the medical and legal professions are regulated). In Denmark, the title of psychologist was legally protected in 1993 so that no one could call themselves a psychologist unless they had received specified training. In Greece, a law was passed in 1979 licensing psychologists to practise (Georgas, 1995). These enlightened views have not extended to some other countries, however, despite the attempts of professional organisations in lobbying their legislators. Finland and the UK have faced obstacles in legalising the profession. The BPS has its own regulatory system so that applied psychologists need to undergo an approved route of training (to go on to practise as forensic, clinical, educational, health psychologists, for example) before they are recognised as qualified professional psychologists by the Society. Most of these individuals choose to register themselves as Chartered Psychologists – a person using the services of a psychologist designated chartered can, therefore, be assured that the person is a recognised professional psychologist.
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(a) (a)
European views of psychology and psychologists
Employment of Danish psychologists No. of psychologists
700 600
1974
500
1983 1994
400 300 200 100
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(b) Employment of psychologists in The Netherlands.
Setting General and mental health care Psychiatric hospitals and clinics Semi-residential mental health care Non-residential mental health care General and academic hospitals Specialised hospitals and clinics Psychogeriatric nursing homes Institution for alcoholics and drug addicts Forensic settings Preventive psychology Private practice
Number of members 1991 1995 441 62 670 448 101 127
511 63 681 523 125 175
58 32 240 991
61 41 498 929
Education and youth care Schools for special education Institutions for educational counselling Homes for the mentally handicapped Children’s homes
68 140 110 44
76 128 107 36
Work Consulting firms Industrial psychologists Vocational guidance
308 242 61
387 206 69
Non-psychologists’ views of what psychology is and what psychologists do are encouragingly positive and generally, accurate although their knowledge of psychological research (as you saw earlier) is flawed. Table 1.5 shows you the responses of an Austrian sample to the question, ‘What do you expect a psychologist to do?’, and to the sentence, ‘Psychologists can . . .’ (Friedlmayer and Rossler, 1995). A Finnish study which asked adults to rate which of a number of professions was more knowledgeable about human nature, found that 53 per cent believed doctors were more knowledgeable, with psychologists following behind in second place (29 per cent) (Montin, 1995). A Norwegian study, however, found the opposite: 49 per cent chose psychologists and 23 per cent chose doctors (Christiansen, 1986). Figures 1.3 (a)–(d) give some of the other illuminating responses to the other questions asked in the Finnish survey. These not only reveal how people
Table 1.5 Austrian views of psychologists (based on a sample of 300 respondents) Statement/question
%
‘Psychologists can . . .’ See through other people Help other people to change Help others to help themselves Exert influence through reports Release people from mental suffering Listen patiently Direct the attention of social policy-makers Handle children well Cause harm by making mistaken diagnoses Make people happier
68 72 90 57 62 88 53 55 68 54
Statement/question
%
Figure 1.2 (a) Areas of employment taken up by Danish psychologists across three decades; (b) employment destinations of members of the Netherlands Institute of Psychology in 1991 and 1995.
What do you expect a psychologist to do?’ Talk Testing Filing a report Treatment/therapy Training children Proposing interventions Negotiating conflicts Giving guidance and advice Solving problems
97 90 85 91 46 86 65 94 44
Sources: (a) Foltveld, P., The psychological profession in Denmark. In A. Schorr and S. Saari (eds) Psychology in Europe; (b) Van Drunen, P., Professional psychology in the Netherlands: history and recent trends. Reproduced with permission from Psychology in Europe, by A. Schorr and S. Saari (eds), ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern
Source: Based on Friedlmayer, S. and Rossler, E., Professional identity and public image of Austrian psychologists. Reproduced with permission from Psychology in Europe by A. Schorr and S. Saari (eds), ISBN 0-88937-155-5,© 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern.
Other School for professional education Universities Research institutes
124 378 32
99 355 15
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(c) ‘How much do you know about psychologists?’
(a) ‘How scientific would you rate a profession to be?’ Nurse
A lot
Social worker
Quite a bit
Economist
A bit
Engineer
Not very much
Teacher
A little
Psychologist
No reply
Psychiatrist 0
Physician No reply
10
20
30
40
50
(d) ‘How did you find out about what psychologists do?’ 0
10
20
30
40
From first-hand experience From second-hand experience
(b) ‘Psychologists are able to read other people’s minds?’
TV Disagree
Radio
Agree
Movies
No reply
Psychology course 0
20
40
60
80
Research literature Newspapers Magazines Fiction Other texts No reply 0
10
20
30
40
50
60
70
Figure 1.3 Responses of a Finnish sample (N = 601) to four questions and statements about psychology. Source: Montin, S. The public image of psychologists in Finland. Reproduced with permission from Psychology in Europe by A. Schorr and S. Saari (eds), ISBN 0-88937-155-5, © 1995, Hogrefe & Huber Publishers, Seattle, Toronto, Göttingen, Bern.
receive or obtain their information about psychology but also show that the discipline is still shrouded in some mystery – 49 per cent declare knowing only ‘a little’ about psychology. Mercifully, 75 per cent of respondents disagreed that psychologists could read minds. You will find the addresses of professional associations and organisations of psychology in Europe at the end of the chapter. You can contact them for more information about postgraduate courses and training opportunities in psychology.
Psychology: the development of a science activit
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Although philosophers and other thinkers have been concerned with psychological issues for cenyp s yc h turies, the science of psychology is comparatively young. To understand how this science came into being, it is useful to trace its roots back through philosophy and the natural sciences. These disciplines originally provided the methods we use to study human behaviour and took many centuries to develop. ee
Philosophical roots of psychology Animism Each of us is conscious of our own existence. Furthermore, we are aware of this consciousness. Although we often find ourselves doing things that we had not planned to do (or had planned not to do), by and large we feel that we are in control of our behaviour. That is, we have the impression that our conscious mind controls our behaviour. We consider alternatives, make plans, and then act. We get our bodies moving; we engage in behaviour. Earlier in human history, philosophers attributed a lifegiving animus, or spirit, to anything that seemed to move or grow independently. Because they believed that the movements of their own bodies were controlled by their minds or spirits, they inferred that the sun, moon, wind, tides and other moving entities were similarly animated. This primitive philosophy is called animism (from the Latin animare, ‘to quicken, enliven, endow with breath or soul’). Even gravity was explained in animistic terms: rocks fell to the ground because the spirits within them wanted to be reunited with Mother Earth. Obviously, animism is now of historical interest only. No educated person believes that rocks fall because they
h syc la
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‘want to’. Rather, we believe that they fall because of the existence of natural forces inherent in physical matter, even if we do not understand what these forces are. But note that different interpretations can be placed on the same events. Surely, we are just as prone to subjective interpretations of natural phenomena, albeit more sophisticated ones, as our ancestors were. In fact, when we try to explain why people do what they do, we tend to attribute at least some of their behaviour to the action of a motivating spirit – namely, a will. In our daily lives, this explanation of behaviour may often suit our needs. However, on a scientific level, we need to base our explanations on phenomena that can be observed and measured objectively. We cannot objectively and directly observe ‘will’. The best means we have to ensure objectivity is the scientific method, which is described in more detail in the next chapter. Psychology as a science must be based on the assumption that behaviour is strictly subject to physical laws, just as any other natural phenomenon is. The rules of scientific research impose discipline on humans whose natural inclinations might lead them to incorrect conclusions. It seemed natural for our ancestors to believe that rocks had spirits, just as it seems natural for people nowadays to believe that behaviour can be affected by a person’s will. In contrast, the idea that feelings, emotions, imagination and other private experiences are the products of physical laws of nature did not come easily; it evolved through many centuries.
Dualism: René Descartes Although the history of Western philosophy properly begins with the Ancient Greeks, a French philosopher and mathematician, René Descartes (1596–1650), is regarded as the father of modern philosophy. He advocated a sober, impersonal investigation of natural phenomena using sensory experience and human reasoning. He assumed that the world was a purely mechanical entity that, having once been set in motion by God, ran its course without divine interference. Thus, to understand the world, one had only to understand how it was constructed. This stance challenged the established authority of the Church, which believed that the purpose of philosophy was to reconcile human experiences with the truth of God’s revelations. To Descartes, animals were mechanical devices; their behaviour was controlled by environmental stimuli. His view of the human body was much the same: it was a machine. Thus, Descartes was able to describe some movements as automatic and involuntary. For example, the application of a hot object to a finger would cause an almost immediate withdrawal of the arm away from the
René Descartes (1596–1650).
source of stimulation. Reactions like this did not require participation of the mind; they occurred automatically. Descartes called these actions reflexes (from the Latin reflectere, ‘to bend back upon itself’). A stimulus registered by the senses produces a reaction that would be entirely physical and beyond voluntary control. There would be no intention or will to produce this physical reaction. Consider the well-known reflex of sensing the heat of a flame, as seen in Figure 1.4. The body recoils from flame in an involuntary way: we do not intentionally move away from the flame but our body reflexively puts in place a chain of muscle contractions which make us withdraw. The term ‘reflex’ is still in use today, but, of course, we explain the operation of a reflex differently, as you’ll see in Chapter 4. What set humans apart from the rest of the world, according to Descartes, was their possession of a mind. This was a uniquely human attribute and was not subject to the laws of the universe. Thus, Descartes was a proponent of dualism, the belief that all reality can be divided into two distinct entities: mind and matter (this is often referred to as Cartesian dualism). He distinguished between ‘extended things’, or physical bodies, and ‘thinking things’, or minds. Physical bodies, he believed, do not think, and minds are not made of ordinary matter. Although Descartes was not the first to propose dualism, his thinking differed from that of his predecessors in one important way: he was the first to suggest that a link exists between the human mind and its purely physical housing. Although later philosophers pointed out that this theoretical link actually contradicted his belief in
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Figure 1.4 Descartes’s diagram of a withdrawal reflex. Source: Image 9902 from Stock Montage, Inc.
dualism, the proposal of an interaction between mind and matter, interactionism, was absolutely vital to the development of the science of psychology. From the time of Plato onwards, philosophers had argued that the mind and the body were different entities. They also suggested that the mind could influence the body but the body could not influence the mind, a little like a puppet and puppeteer with the mind pulling the strings of the body. Not all philosophers adopted this view, however. To some, such as Spinoza (1632–1677), both mental events (thinking) and physical events (such as occupying space) were characteristic of one and the same thing, in the same way that an undulating line can be described as convex or concave – it cannot be described as exclusively one thing or another (this is called double-aspect theory). Descartes hypothesised that this interaction between mind and body took place in the pineal body, a small organ situated on top of the brain stem, buried beneath the large cerebral hemispheres of the brain. When the mind decided to perform an action, it tilted the pineal body in a particular direction, causing fluid to flow from the brain into the proper set of nerves. This flow of fluid caused the appropriate muscles to inflate and move. How did Descartes come up with this mechanical concept of the body’s movements? Western Europe in the seventeenth century was the scene of great advances in the sciences. This was the century, for example, in which William Harvey discovered that blood circulated around
the body. It was not just the practical application of science that impressed Europeans, however, it was the beauty, imagination and fun of it as well. Craftsmen constructed many elaborate mechanical toys and devices during this period. The young Descartes was greatly impressed by the moving statues in the Royal Gardens (Jaynes, 1970) and these devices served as models for Descartes as he theorised about how the body worked. He conceived of the muscles as balloons. They became inflated when a fluid passed through the nerves that connected them to the brain and spinal cord, just as water flowed through pipes to activate the statues. This inflation was the basis of the muscular contraction that causes us to move. This story illustrates one of the first examples of a technological device used to model and explain how the nervous system works. In science, a model is a relatively simple system that works on known principles and is able to do at least some of the things that a more complex system can do. For example, when scientists discovered that elements of the nervous system communicate by means of electrical impulses, researchers developed models of the brain based on telephone switchboards and, more recently, computers. Abstract models, which are completely mathematical in their properties, have also been developed. Clinical psychologists may interpret mental disorder according to a medical model which conceives of clinical mental disturbance as an illness. Although Descartes’s model of the human body was mechanical, it was controlled by the non-mechanical (in fact, non-physical) mind. Thus, humans were born with a special capability that made them greater than simply the sum of their physical parts. Their knowledge was more than merely a physical phenomenon. Descartes’s influence on the development of psychology was considerable. He proposed the revolutionary idea that the mind and the body were mutually interacting and suggested a method of studying ‘the mind’ which was based on reasoning and not metaphysical analysis. Descartes’s notion of interactionism gave rise to two very influential but very different schools of thought in psychology at the end of the nineteenth and the beginning of the twentieth centuries: introspectionism and behaviourism. We consider these later in the chapter.
Empiricism: John Locke and David Hume With the work of the English philosopher John Locke (1632–1704), the mechanisation of the whole world became complete. Locke did not exempt the mind from the mechanical laws of the material universe. Descartes’s rationalism – pursuit of truth through reason – was replaced by empiricism – pursuit of truth through observation and experience (in Greek, empeiria means experience).
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A prevalent belief in the seventeenth century was that ideas were innately present in an infant’s mind. Locke rejected this belief. Instead, he proposed that all knowledge must come through experience: it is empirically derived. His model of the mind was a tablet of soft clay, a tabula rasa, smooth at birth and ready to accept the writings of experience imprinted upon it. Locke believed that our knowledge of complex experiences was nothing more than links between simple, primary sensations: simple ideas combined to form complex ones. This notion was developed further by the Scottish philosopher David Hume (1711–76). In his book A Treatise of Human Nature (1739), Hume argued that the study of human nature could best be undertaken through experience and observation. Hume’s conception of the mind was slightly different from that of Locke. Whereas Locke wrote of ideas, Hume wrote of perceptions which were composed of impressions and ideas. Impressions were what we would consider sensations – seeing print on a paper or hearing a loud bang; ideas were the less vivid recollection of such sense experiences. Impressions, according to Hume, were the most important perceptions because these were derived directly from observation. Any ideas based on content which was not derived empirically were not valuable and not trustworthy. Hume, therefore, espoused what is known as positivism – the school of thought which argues that all meaningful ideas can be reduced to observable material. Perhaps Hume’s greatest contribution to psychology was the doctrine of the association of ideas. In An Inquiry Concerning Human Understanding (1748), Hume argued that there were various types of connection or association between ideas. This was not itself a new idea. Aristotle had proposed the notion of an association of ideas: two stimuli if paired frequently enough would result in the presentation of one event stimulating thoughts of the other. Hume suggested three specific types of association: resemblance (when we look at someone’s photograph, for example, this triggers off thoughts about that person), contiguity (thoughts of an object or event will trigger thoughts related to those objects and events), and cause and effect (the idea that actions have identifiable causes). These associations were the ‘cement’ that helped bind the universe, and all complex human experiences were based on simple ideas derived from impressions. The most important of these associations was cause and effect, and Hume developed this theme by describing behaviour in terms of custom and habit. According to Hume, if one performs an act which produces an effect which makes a repetition of that act likely, this is a habit or custom. For example, think of a simple behaviour such as switching on a light. Your knowledge that switching a light on will illuminate a room will result in your habitually pressing the switch if you need light.
These notions of habit and causality became very important in the twentieth century with the development of behaviourism and the work of the Swiss developmental psychologist Jean Piaget (1896–1980), described later.
Idealism: Bishop Berkeley In contrast to the empiricists, the Irish bishop, philosopher and mathematician George Berkeley (1685–1753) believed that our knowledge of events in the world did not come simply from direct experience. Instead, Berkeley (who gave his name to the famous university in California) argued that this knowledge is the result of inferences based on the accumulation of past experiences derived through the senses. In other words, we must learn how to perceive. For example, our visual perception of depth involves several elementary sensations, such as observing the relative movements of objects as we move our head and the convergence of our eyes (turning inward towards each other or away) as we focus on near or distant objects. Although our knowledge of visual depth seems to be immediate and direct, it is actually a secondary, complex response constructed from a number of simple elements. Our perceptions of the world can also involve integrating the activity of different sense organs, such as when we see, hear, feel and smell the same object. The aspect of Berkeley’s philosophy which argues that all ideas come from the senses (esse est percipi) is called idealism. As you can see, the philosophers Locke, Hume and Berkeley were grappling with the workings of the human mind and the way in which people acquire knowledge. They were dealing with the concept of learning. Modern psychologists are still concerned with the issues that Berkeley raised. As philosophers, they were trying to fit a non-quantifiable variable – reason – into the equation.
Materialism: James Mill With the work of the Scottish philosopher James Mill (1773–1836), the pendulum took its full swing from animism (physical matter animated by spirits) to materialism (mind composed entirely of matter). Materialism is the belief that reality can be known only through an understanding of the physical world, of which the mind is a part. Mill worked on the assumption that humans and animals were fundamentally the same. Both humans and animals were thoroughly physical in their make-up and were completely subject to the physical laws of the universe. He agreed in essence with Descartes’s approach to understanding the human body but rejected the concept of an immaterial mind. Mind, to Mill, was as passive as the body. It responded to the environment in precisely the same way. The mind, no less than the body, was a machine.
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In the nineteenth century, the philosophy of the past began to make way for the experimentation of the future. In the latter part of the century, a part of Germany gave birth to modern psychology as we know it. Its midwife was Wilhelm Wundt.
Modern psychology: from the Leipzig laboratory to the cognitive revolution Wilhelm Wundt (1832–1920) was the first person to call himself a psychologist and he shared the conviction of other German scientists that all aspects of nature, including the human mind, could be studied scientifically, an approach summarised in his book Principles of Physiological Psychology, the first textbook in psychology. Wundt’s approach was experimental in nature and his and his colleagues’ work was conducted at the Leipzig laboratory. Over one hundred studies were conducted in the first twenty years of the laboratory’s life. Initially, these were studies of the psychological and psychophysiological aspects of vision (seeing), audition (hearing) and somatosensation (feeling and touching). Later work focused on reaction time and the process involved in perceiving and then responding to a stimulus. Wundt also explored the nature of attention and emotional feeling as well as word association. The fact that Germany was the birthplace of psychology had as much to do with social, political and economic influences as with the abilities of its scientists and scholars. The German university system was well established, and professors were highly respected members of society. The academic tradition in Germany emphasised a scientific approach to a large number of subject areas, such as history, phonetics, archaeology, aesthetics and literature. Thus, in contrast to French and British scholars, who adopted the more traditional, philosophical approach to the study of the human mind, German scholars were open to the possibility that the human mind could be studied scientifically. Experimental physiology, one of the most important roots of experimental psychology, was well established there. Eventually, Wundt’s influence began to extend to other parts of Europe (especially the UK) and to the USA.
ideas and sensations. These elements could be constructed into a table of elements similar to a chemical table of elements. Structuralism’s raw material was supplied by trained observers who described their own experiences under well-controlled conditions. The observers were taught to engage in introspection (literally, ‘looking within’), the use of which was governed by strict rules. Introspectionists observed stimuli and described their experiences. According to Boring (1953), observers participating in reaction time experiments had to produce approximately 10,000 introspective observations before their data were considered valid and they themselves considered to be qualified introspectionists. Wundt’s aims were threefold: to analyse the contents of conscious experience, to determine how the elements of consciousness are connected, and to devise a law which would explain such connections. Wundt and his associates, Edward Tichener (1867–1927) and Gustav Fechner (1801– 87), made inferences about the nature of mental processes by seeing how changes in the stimuli caused changes in the verbal reports of their trained observers. Wundt was particularly interested in the problem that had intrigued Berkeley: how did basic sensory information give rise to complex perceptions? His doctrine of apperception attempted to account for the fact that when we perceive, this perception is of a whole object and not separate elements of it. We see wholes, according to Wundt, because of the process of creative synthesis (or law of psy-
Structuralism: Wilhelm Wundt Wundt defined psychology as the ‘science of immediate experience’, and his approach was called structuralism, the first proper school of thought to emerge in the history of psychology. Its subject matter was the structure of the mind, built from the elements of consciousness, such as
Wilhelm Wundt (1832–1920).
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chic resultants): a process which combines or synthesises elements to form a whole. Again, this process is very similar to a process in chemistry in which individual chemical elements when combined will form a new, wholly different entity. The whole would not be equivalent to the sum of its parts. Much of Wundt’s work, however, aimed to break down and analyse the contents of the mind rather than determine how they are combined. Wundt was an ambitious and prolific scientist who wrote many books and trained many other scientists in his laboratory. However, his method did not survive the test of time; structuralism died out in the early twentieth century. The major problem with his approach was the difficulty encountered by observers in reporting the raw data of sensation, data unmodified by experience. Although introspectionism aimed to establish well-controlled experimental conditions which would lead to reliable introspective observations, there was often little agreement between observers about their introspections. The method has also been criticised for its reliance on retrospection; the recollection of an experience was frequently elicited some time after the experience itself had occurred and was, therefore, subject to error. In addition, attention began to shift from study of the human mind to the study of human behaviour. Behaviourism provided a devastating and critical alternative to introspectionism. According to behaviourism’s founding father, the American John B. Watson, introspectionism was akin to superstition, an argument considered in detail a little later on. Recently, psychologists have resumed the study of the human mind, but we now have better methods for studying it than were available to Wundt. Although structuralism has been supplanted, Wundt’s contribution must be acknowledged. He was responsible for establishing psychology as a recognised, experimental science that was separate from philosophy. He used methods which involved observation and experimentation and trained a great number of psychologists, many of whom established their own schools and continued the evolution of the new discipline.
Intrigued by Fechner’s research, Ebbinghaus decided to attempt to measure human memory: the processes of learning and forgetting. Working alone, Ebbinghaus devised methods to measure memory and the speed with which forgetting occurred. He realised that he could not compare the learning and forgetting of two prose passages or two poems because some passages would undoubtedly be easier to learn than others. Therefore, he devised a relatively uniform set of materials – nonsense syllables, such as ‘juz’, ‘bul’ and ‘gof’. He printed the syllables on cards and read through a set of them, with the rate of presentation controlled by the ticking of a watch. After reading the set, he paused a fixed amount of time, then read the cards again. He recorded the number of times he had to read the cards to be able to recite them without error. He measured forgetting by trying to recite the nonsense syllables on a later occasion – minutes, hours or days later. The number of syllables he remembered was an index of the percentage of memory that had been retained. Ebbinghaus’s approach to memory was entirely empirical; he devised no theory of why learning occurs and was interested only in gathering facts through careful, systematic observation. However, despite the lack of theory, his work made important contributions to the development of the science of psychology. He introduced the principle of eliminating variable errors by making observations repeatedly on different occasions (using different lists each time) and calculating the average of these observations. Variable errors include errors caused by random differences in the subject’s mood or alertness or by uncontrollable changes in the environment. He constructed graphs of the rate at which the memorised lists of nonsense syllables were forgotten, which provided a way to measure mental contents across time. As you will see in Chapter 8, Ebbinghaus’s research provided a model of systematic, rigorous experimental procedures that modern psychologists still emulate.
Memory: Hermann Ebbinghaus
Functionalism: William James and James Angell
Most of the pioneers of psychology founded schools, groups of people having a common belief in a particular theory and methodology. In this context, the word school refers to a branch of a particular academic discipline, not a building or institution. Structuralism was a school of psychology. The exception to this trend was Hermann Ebbinghaus (1850–1909). In 1876, after receiving his Ph.D. in philosophy but still unattached to an academic institution, Ebbinghaus came across a second-hand copy of a book by Gustav Fechner describing a mathematical approach to the measurement of human sensation.
After structuralism, the next major trend in psychology was functionalism. This approach, which began in the USA, was in large part a protest against the structuralism of Wundt. Structuralists were interested in what they called the components of consciousness (ideas and sensations); functionalists were more interested in the process of conscious activity (perceiving and learning). Functionalism grew from the new perspective on nature provided by Charles Darwin and his followers. Proponents of functionalism stressed the biological significance (the purpose, or function) of natural processes,
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ism’s adaptation to the environment and are a product of its evolutionary history. For example, the fact that we are conscious implies that consciousness has adaptive value for our species.
• Functional psychology studies the relation between the environment and the response of the organism to the environment. There is no meaningful distinction between mind and body, they are part of the same entity.
Evolution and heritability: Charles Darwin and Francis Galton
William James (1842–1910).
including behaviours. The emphasis was on overt, observable behaviours, not on private mental events. The most important psychologist to embrace functionalism was William James (1842–1910), brother of novelist Henry. As James said, ‘My thinking is first, last, and always for the sake of my doing.’ That is, thinking was not an end in itself; its function was to produce useful behaviours. Although James was a champion of experimental psychology, he did not appear to enjoy doing research, instead spending most of his time reading, thinking, teaching and writing during his tenure as professor of philosophy (later, professor of psychology) at Harvard University. Unlike structuralism, functionalism was not supplanted; instead, its major tenets were absorbed by its successor, behaviourism. One of the last of the functionalists, James Angell (1869–1949), described its basic principles:
• Functional psychology is the study of mental operations and not mental structures. It is not enough to compile a catalogue of what the mind does; one must try to understand what the mind accomplishes by doing this. • Mental processes are not studied as isolated and independent events but as part of the biological activity of the organism. These processes are aspects of the organ-
Charles Darwin (1809–82) proposed the theory of evolution in his book On the Origin of Species by Means of Natural Selection, published in 1859. His work, more than that of any other person, revolutionised biology. The concept of natural selection showed how the consequences of an animal’s characteristics affect its ability to survive. Instead of simply identifying, describing and naming species, biologists began now to look at the adaptive significance of the ways in which species differed. Darwin’s theory suggested that behaviours, like other biological characteristics, could best be explained by understanding their role in the adaptation of an organism (a human or other animal) to its environment. Thus, behaviour has a biological context. Darwin assembled evidence that behaviours, like body parts, could be inherited. In The Expression of the Emotions in Man and Animals, published in 1873, he proposed that the facial gestures that animals make in expressing emotions were descended from movements that previously had other functions. New areas of exploration were opened for psychologists by the ideas that an evolutionary continuity existed among the various species of animals and that behaviours, like parts of the body, had evolutionary histories. Darwin’s notion of natural selection has had great impact on the way in which we view the genetic determinants of behaviour (as Chapter 3 will show). One of the first psychologists to study the influence of genetics on human behaviour was Sir Francis Galton (1822–1911), Darwin’s first cousin. Galton was a polymath who made many other contributions to the field of science: he constructed the first weather maps of the British Isles, discovered and named the weather phenomenon we know as anticyclone, invented the term ‘correlation’ (which describes the statistical relationships between two variables or factors), developed the technique of fingerprinting, founded the discipline of psychometrics, which applies statistical principles to the measurement of individual differences and the construction of psychological tests, and established the Anthropometric Laboratory in London in 1884, the birthplace of intelligence testing.
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Galton was interested in discovering whether people’s physical features correlated with each other and whether such correlations occurred for psychological features such as sensory capacity, reaction time, intellect and eminence. In fact, Galton did find that features such as height, arm length and weight were highly and positively correlated and argued from this that if one part of the body’s dimensions were known then one could construct the rest of the body to scale. Importantly, Galton was the first to provide statistical evidence for the heritability of psychological variables. In his study of eminent men, published in his book Hereditary Genius (Galton, 1869), Galton found that 31 per cent of illustrious men had eminent fathers and 48 per cent of these men had eminent sons. Of course, by today’s standards, this study has several methodological shortcomings, not least of which is the collection of data from eminent men only (to make a valid comparison, you would also need to look at non-eminent men and their offspring). There is also the argument that eminence may not have been inherited but had been determined by the environment in which these men were raised (issues discussed in detail in Chapters 3 and 11). However, Galton remains an important figure in the history of psychology. His greatest contribution is the establishment of the study of individual differences as a scientific enterprise.
(a)
(b)
Psychodynamic theory: Sigmund Freud While psychology was developing as a fledgling science, Sigmund Freud (1856–1939) was formulating a theory of human behaviour that would greatly affect psychology and psychiatry (not necessarily for the good) and radically influence intellectual thinking of all kinds. Freud began his career as a neurologist, so his work was originally firmly rooted in biology. He soon became interested in behavioural and emotional problems and began formulating his psychodynamic theory of personality, which would evolve over his long career. Although his approach was based on observation of patients and not on scientific experiments, he remained convinced that the biological basis of his theory would eventually be established. Freud and his theory are discussed in detail in Chapter 14 (Personality) but he is mentioned here to mark his place in the history of psychology. His theory of the mind included structures, but his structuralism was quite different from Wundt’s. He devised his concepts of ego, superego, id and other mental structures through talking with his patients, not through laboratory experiments. His hypothetical mental operations included many that were unconscious and hence not available to introspec-
(c) The three most widely cited psychologists of the 20th century: (a) Sigmund Freud; (b) Jean Piaget; (c) Hans J. Eysenck. Source: (a) National Library of Medicine/Science Photo Library Ltd.; (b) AFP/Getty Images; (c) Popperfoto/Alamy Images.
tion. And unlike Wundt, Freud emphasised function; his mental structures served biological drives and instincts and reflected our animal nature. For better or worse Freud’s name is the one most closely allied to psychology in the mind of the public. In a recent study of the most eminent psychologists, as measured by citations in journals, introductory textbooks and nominations from self-selecting members of the American Psychological Society via an email survey, Hagbloom et al. (2002) found that Freud was the most widely cited author in the discipline, as you can see in Tables 1.6 a–c. In second place was Jean Piaget and in third, Hans J. Eysenck.
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Table 1.6. The top ten psychologists (a) cited in the professional literature, (b) named as eminent by the American Psychological Society, and (c) most frequently cited in introductory textbooks. (a) Rank
Name
1 2 3 4 5 6 7 8 9 10
Sigmund Freud Jean Piaget Hans J. Eysenck B.J. Winer Albert Bandura S. Siegel Raymond B. Cattell B.F. Skinner Charles E. Osgood J.P. Guilford
Citation frequency 13 890 8 821 6 821 6 206 5 831 4 861 4 828 4 339 4 061 4 006
(b) Rank
Name
1 2 3 4 5 6.5 6.5 8 9.5 9.5
B.F. Skinner Jean Piaget Sigmund Freud John B. Watson Albert Bandura William James Ivan P. Pavlov Kurt Lewin/Roger Brown Carl Rogers Edward Thorndike
Citation frequency 58 33 28 24 23 21 21 17 14 14
Behaviourism: Edward Thorndike and Ivan Pavlov The next major trend in psychology, behaviourism, followed directly from functionalism. It went further in its rejection of the special nature of mental events, denying that unobservable and unverifiable mental events were properly the subject matter of psychology. Behaviourists believed that because psychology is the study of observable behaviours, mental events – which cannot be observed – are outside the realm of psychology. Behaviourism is thus the study of the relation between people’s environments and their behaviour; what occurs within their heads is irrelevant. One of the first behaviourists was Edward Thorndike (1874–1949), an American psychologist who studied the behaviour of animals. He noticed that some events, usually those that one would expect to be pleasant, seemed to ‘stamp in’ a response that had just occurred. Noxious events seemed to ‘stamp out’ the response, or make it less likely to recur. We now call these processes reinforcement and punishment, and they are described in more detail in Chapter 7 (Learning and behaviour). Thorndike defined the law of effect as follows (1905, p. 203):
Any act which in a given situation produces satisfaction becomes associated with that situation, so that when the situation recurs the act is more likely than before to recur also. Conversely, any act which in a given situation produces discomfort becomes disassociated from that situation, so that when the situation recurs the act is less likely than before to recur.
(c) Rank
Name
1 2 3 4 5 6 7 8 9 10
Sigmund Freud B.F. Skinner Albert Bandura Jean Piaget Carl Rogers Stanley Schachter Harry F. Harlow Roger Brown Neal E. Miller D.C. McClelland
Citation frequency 560 310 303 240 202 200 175 162 154 153
Source: Hagbloom, S.J., Warnick, R., Warnick, J.E., Jones, V.K., Yarbrough, G.L., Russell, T.M., Borecky, C.M., McGahhey, R., Powell, J.L., Beavers, J. and Monte, E., The 100 most eminent psychologists of the 20th century. Review of General Psychology, 2002, 6, 139–52, copyright © 2002 by the Educational Publishing Foundation, reprinted with permission.
The law of effect is in the functionalist tradition. It observes that the consequences of a behaviour act back upon the organism, affecting the likelihood that the behaviour that just occurred will occur again. An organism does something, and the consequences of this action make that action more likely. This process is very similar to the principle of natural selection. Just as organisms that successfully adapt to their environments are more likely to survive and breed, behaviours that cause useful outcomes are more likely to recur. Although Thorndike insisted that the subject matter of psychology was behaviour, his explanations contained mentalistic terms. For example, in his law of effect he spoke of ‘satisfaction’, which is certainly not a phenomenon that can be directly observed. Later behaviourists threw out terms like ‘satisfaction’ and ‘discomfort’ and
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1919). Watson was a charismatic professor of psychology at the Johns Hopkins University in the US, a popular teacher and writer and was a very convincing advocate of behaviourism. Even after leaving Johns Hopkins under mysterious circumstances and embarking on a highly successful career in advertising, he continued to lecture and write magazine articles about psychology. According to Watson, psychology was a natural science whose domain was restricted to observable events: the behaviour of organisms. Watson’s behaviourism can be best summed up by his definition published in an article entitled, ‘Psychology as the behaviorist views it’ (Watson, 1913):
Ivan Pavlov (1849–1936) in his laboratory with some of his collaborators. His research revealed valuable, though unsought, information about the principles of learning. Source: Bettman/CORBIS, reprinted by permission.
replaced them with more objective terms that reflected the behaviour of the organism rather than any feelings it might have. Another major figure in the development of behaviourism was not a psychologist but a physiologist: Ivan Pavlov (1849–1936), a Russian who studied the physiology of digestion (for which he later received a Nobel Prize). In the course of studying the stimuli that produce salivation, he discovered that hungry dogs would salivate at the sight of the attendant who brought in their dishes of food. Pavlov found that a dog could be trained to salivate at completely arbitrary stimuli, such as the sound of a bell, if the stimulus was quickly followed by the delivery of a bit of food into the animal’s mouth. Pavlov’s discovery had profound significance for psychology. He showed that through experience an animal could learn to make a response to a stimulus that had never caused this response before. This ability, in turn, might explain how organisms learn cause-and-effect relations in the environment. In contrast, Thorndike’s law of effect suggested an explanation for the adaptability of an individual’s behaviour to its particular environment. So, from Thorndike’s and Pavlov’s studies two important behavioural principles had been discovered.
Psychology as the behaviorist views it is a purely objective experimental branch of natural science. Its theoretical goal is the prediction and control of behavior. Introspectionism forms no essential part of its methods, nor is the scientific value of its data dependent upon the readiness with which they lend themselves to interpretation in terms of consciousness. The behaviorist, in his efforts to get a unitary scheme of animal response, recognises no dividing line between man and brute.
Watson believed that the elements of consciousness studied by structuralists were too subjective to lend themselves to scientific investigation. He defined psychology as the objective study of behaviour and the stimuli which produce such behaviour. The important feature of behaviourism was its reliance only on observable behaviour. Even thinking was reduced to a form of behaviour –
Behaviourism: John B. Watson Behaviourism as a formal school of psychology began with the publication of a book by John B. Watson (1878–1958), Psychology from the Standpoint of a Behaviorist (Watson,
John B. Watson (1878–1958). Source: Archives of the History of American Psychology.
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talking to oneself. Watson described visually observable behaviour as ‘explicit behaviour’ and those behaviours which could not be directly observed but potentially observed as ‘implicit behaviour’. For example, we cannot see the body’s cells transmitting electrical signals but we can observe such behaviour by using the correct electrical recording equipment. Another important feature, tied to observation, was that the brain had very little to do with what was directly observed. What was important to Watson was the concept of stimulus and response, an idea suggested by Descartes and explicitly described by Pavlov. Watson argued that, given the correct stimuli, the organism could learn to behave (give responses) in a specific way (in the same way that Pavlov’s dogs had ‘learned’ to associate the bell with the appearance of food). Watson, however, famously went further. In his book Behaviorism (1930), he argued:
Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select – doctor, lawyer, artist, merchant-chief and, yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors.
Many of Watson’s ideas, such as the notion that reflexes can be conditioned, have been incorporated into the mainstream of psychology, although the central tenet that all behaviour that is studied must be observable, has not. After Watson, a new form of behaviourism emerged which took Watson’s ideas and developed them further. This new form became known as neobehaviourism or radical behaviourism.
Radical behaviourism: Edward Tolman and Clark Leonard Hull The period 1930–1960 saw a tremendous surge not only in the description of the ways in which organisms behaved but also in the explanations for why they behaved in the way they did. This surge was generated largely by the work of a group of American psychologists, Edward Tolman (1886–1959), Clark Leonard Hull (1884–1952) and B.F. Skinner (1904–1990). Each had a different view on how behaviour occurred but all used animal experiments and the procedures of learning experiments to support their theories. Hull, for example, proposed a highly detailed mathematical model of behaviour, based on his conditioning work with rats in his book Principles of Behavior (Hull, 1943), which sought
to explain almost all behaviour. The basic feature of Hull’s model was that all human (and any organism’s) behaviour evolves through interaction with the environment. However, this interaction occurs within a wider frame of reference – the biological adaptation of the organism to the environment. The variable intervening between environment and organism was drive – a bodily need arising from deprivation or desire or another motivational spur. Although one of the more widely cited psychologists of his day, Clark has not made a lasting impact on psychology largely because his extremely detailed mathematical analyses were based on few experiments, the results of which were generalised well beyond the scope of the experimental context. Tolman suggested that it was important not only to observe the stimulus and response but to take into account intervening variables. To Tolman, these intervening variables were cognitions and demands, and Tolman’s theory became known as purposive behaviourism, so-called because all behaviour was goal-directed and had a purpose. Tolman’s work did not bequeath any major principles or laws, however, although interest in his work continues (Reid and Staddon, 1998). You will find out more about Hull’s and Tolman’s approaches in Chapter 7.
Radical behaviourism: Burrhus Frederic Skinner The bequest of a major framework of thinking in psychology was left to B.F. Skinner (1904–1990), one of the most influential psychologists of the twentieth century whose entry into psychology’s history was serendipitous (he originally wanted to be a writer, and actually wrote novels using his research ideas). Skinner’s work gave birth to the technology of teaching machines (which have since been replaced by computers), the use of behaviour modification in instruction of the mentally retarded, and the use of behaviour therapy to treat mental disorders. Skinner’s work focused on the idea of reinforcement and was based largely on observation of behaviour in pigeons. He found that a certain set of stimulus conditions (such as a box, hunger, food in sight) would elicit certain behaviours (strutting, random pecking). If the animal behaved in a certain way to obtain food then the food became the reinforcing stimulus or the reinforcer – a stimulus which increases the probability that behaviour will occur again. Using his observations of pigeons’ behaviour, Skinner found that the pigeons could be trained to behave in a specific way when responding to specific signals from their environment. For example, the pigeon would learn that it would receive food only if it pecked a food-dispensing lever a certain number of times; instead of randomly pecking at this lever it would then peck only the number of times necessary.
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Psychologists, including modern behaviourists, have moved away from the strict behaviourism of Watson and Skinner; mental processes such as imagery and attention are again considered to be proper subject matter for scientific investigation. But Watson’s emphasis on objectivity in psychological research remains. Even those modern psychologists who most vehemently protest against what they see as the narrowness of behaviourism use the same principles of objectivity to guide their research.
Genetic epistemology: Jean Piaget
B.F. Skinner (1904–90).
This form of learning, instrumental or operant learning, was of three types. Positive reinforcement refers to pleasant reinforcers such as the attention or approval given to a child from a teacher. Punishment refers to a negative stimulus which is presented when a behaviour occurs (for example, a rat receiving an electric shock whenever it presses a lever). Negative reinforcement refers to a behaviour which reduces the likelihood of negative stimulation (for example, a rat pressing a lever to avoid electric shock). Reinforcement could also occur according to scheduling. For example, fixed-interval reinforcement involved a reinforcer that was given only after a set time; fixed-ratio reinforcement involved a reinforcer that was given only after a predetermined number of responses. Examples of fixed-interval reinforcement include receiving a wage at the end of the week or a salary at the end of the month; an example of fixed-ratio reinforcement would be the delivery of payment after, say, a certain number of items had been produced in a factory or after a specific number of products had been sold. Chapter 7 takes up these ideas. Unlike Tolman and Hull, however, Skinner did not propose any intervening variables. To him, the behaving person or pigeon or rat was an ‘empty organism’. He argued that humans were machines which behaved in lawful and predictable ways and his system was almost entirely descriptive with little in the way of theory emerging from it. In addition to his scientific work, Skinner published a novel, Walden Two, in which he described the way in which radical behaviourism could operate (Skinner, 1948).
While American approaches to psychology were dominated by the new behaviourism, a different approach to the study of cognitive function was being espoused in Europe. The Swiss psychologist Jean Piaget (1896–1980) became interested in the question of human knowledge and how we begin to acquire knowledge. He believed that answers to such questions could be obtained by empirical, scientific research and he would measure the development of the acquisition of knowledge in children by presenting them with intellectual tasks at various stages of their lives (in fact, Piaget had worked with Theophile Simon, the collaborator of the man who designed the first IQ test, Alfred Binet). Piaget termed his approach to psychology as genetic epistemology: the study of the origin of knowledge in child development. Apart from Piaget’s focus on the acquisition of knowledge in groups of individuals, another difference between his European approach and that of his American counterparts was the lack of interest in the applied nature of research. Questions regarding the possibility of improving or accelerating children’s learning did not interest Piaget, nor did it interest other European researchers (Leahey, 2003). Although his work made little impact on psychology at the time, the subsequent circulation of his work – with translations of his books – led to a considerable interest in his research (Smith, 1996), so much so, that few psychologists have dominated the study of child development in the way that Piaget has. Piaget’s contribution to our understanding of child cognition is assessed in Chapter 12.
Gestalt psychology: Max Wertheimer The structuralism of Wilhelm Wundt was not the only German influence on the development of psychology. In 1911, a German psychologist, Max Wertheimer (1880– 1943), bought a toy that presented a series of pictures in rapid succession. Each picture was slightly different from the one that preceded it, and the resulting impression was that of continuous motion, like a film. Wundt and his followers insisted that if we want to understand the nature of
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human consciousness we must analyse it – divide it into its individual elements. But Wertheimer and his colleagues realised that the perception of a motion picture was not that of a series of individual still pictures. Instead, viewers saw continuity in time and space. They saw objects that retained their identity as they moved from place to place. Asking people to study these pictures one at a time and to describe what they saw (the structuralist approach) would never explain the phenomenon of the motion picture. Wertheimer and his colleagues attempted to discover the organisation of cognitive processes, not their elements. They called their approach Gestalt psychology. Gestalt is a German word that roughly translates into ‘unified form’ or ‘overall shape’. Gestalt psychologists insisted that perceptions resulted from patterns of interactions among many elements – patterns that could exist across both space and time. For example, a simple melody consists of a pattern of different notes, played one at a time. If the melody is played in different keys, so that the individual notes are different, people can still recognise it. Clearly, they recognise the relations the notes have to each other, not just the notes themselves. Although the Gestalt school of psychology no longer exists, its insistence that elements of an experience interact – that the whole is not simply the sum of its parts – has had a profound influence on the development of modern psychology. Gestalt psychology did not disappear because of some inherent fatal flaw in its philosophy or methodology. Instead, many of its approaches and ideas were incorporated into other areas of psychology. Gestalt psychology is discussed in more detail in Chapter 6.
Humanistic psychology Humanistic psychology developed during the 1950s and 1960s as a reaction against both behaviourism and psychoanalysis. Although psychoanalysis certainly dealt with mental phenomena that could not be measured objectively, it saw people as products of their environment and of innate, unconscious forces. Humanistic psychologists insist that human nature goes beyond environmental influences, and that conscious processes, not unconscious ones, are what psychologists should study. In addition, they note that psychoanalysis seems preoccupied with mental disturbance, ignoring positive phenomena such as happiness, satisfaction, love and kindness. Humanistic psychology is an approach to the study of human behaviour that emphasises human experience, choice and creativity, self-realisation and positive growth. The father of humanistic psychology, Abraham Maslow (1908–1970), wrote: ‘What a man can be, he must be. He must be true to his own nature . . . [to a] desire to become more and more what one idiosyncratically is, to become everything that one is capable of becoming’ (1970, p. 46).
Humanistic psychologists emphasise the positive sides of human nature and the potential we all share for personal growth. In general, humanistic psychologists do not believe that we will understand human consciousness and behaviour through scientific research. Thus, the humanistic approach has not had a significant influence on psychology as a science. Its greatest impact has been on the development of methods of psychotherapy based on a positive and optimistic view of human potential.
The personality psychologists: Gordon Allport, Raymond Cattell, Hans Eysenck, Walter Mischel, Paul Costa and Robert McCrae As the humanist movement was in full swing – or as swinging as it could manage – experimental psychologists had turned their attention to the scientific measurement of another important facet of behaviour: personality. This attention took the form of a search for universal personality traits – enduring personal characteristics which form a continuum along which we all fall. The earliest of these theorists was Gordon Allport (1897–1967) who, using dictionary terms as his starting point, suggested that personality comprised between 3 and 16 personality traits. Allport’s scheme formed the basis for the model devised by Raymond Cattell (1905–1998). He collected data from interviews and various questionnaires, concluding that 16 personality traits comprised the essence of personality. A more parsimonious account, based on a statistical technique called factor analysis, was proposed by Hans J. Eysenck (1916–1997). In what was, until recently, one of the most widely accepted views of personality traits, Eysenck proposed that personality comprised three dimensions: neuroticism–stability, extraversion–intraversion and psychoticism–normality, all of which had a biological basis. Each of us scores somewhere along all three dimensions. Meanwhile, influential American psychologists such as Walter Mischel (1930– ) argued that traits did not exist and that, when we behave, we are reacting to changes in our environment or situation (this approach is called situationism): that we may respond in a consistent way lulls us into thinking that we possess something called ‘personality’, characterised by a number of traits. The debate continues, but the situationists seem to be fighting a losing battle. Substantial research supported Eysenck’s model but this was usurped in the 1980s by the Five Factor Model of Paul T. Costa and Robert R. McCrae. This, now the most widely accepted view of personality, argues that our personality comprises five traits which we possess to varying degrees: agreeableness, conscientiousness, extraversion, neuroticism and openness to experience. You’ll find more information on all of these approaches in Chapter 14.
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Paul T. Costa.
A photograph of Milgram’s experiment.
Source: Bo Mathisen
Source: Getty Images/Hulton Archive
The social psychologists From the middle of the twentieth century there also appeared a phenomenal body of research into how we view and influence other individuals. Here, there are too many significant figures to mention but some of the most
prominent that contributed significant new data and models which helped us understand social behaviour include Leon Festinger, Albert Bandura, Stanley Milgram, Philip Zimbardo, Elliot Aronson, Robert Zajonc, Richard Nisbett and Edward Jones. All Americans or working in the US, these psychologists demonstrated how we could
Robert R. McCrae.
Philip Zimbardo.
Source: Robert McCrae
Source: Corbis: Lynn Goldsmith
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hold two seemingly contradictory views (Festinger), how deindividuation could strip us of our humanity (Zimbardo), how observation of others makes us imitate them (Bandura), how we become obedient to authority (Milgram), how we interpret the causes of our own behaviour differently from how we interpret that of others (Nisbett, Jones), amongst other things. You’ll find descriptions of their research and the impact this has had on our understanding of social behaviour in Chapters 15 and 16.
The cognitive revolution: beyond behaviourism The emphasis on behaviourism in the first half of the twentieth century restricted the subject matter of psychology to observable behaviours. For many years, concepts such as consciousness were considered to be outside the domain of psychology. As one psychologist put it, ‘psychology, having first bargained away its soul and then gone out of its mind, seems now . . . to have lost all consciousness’ (Burt, 1962, p. 229). In the decades that followed many psychologists protested against the restrictions of behaviourism and turned to the study of consciousness, feelings, memory, imagery and other private events (although behaviourism was still a potent force and continues to runs through much of today’s experimental psychology like marble).
Much of cognitive psychology uses an approach called information processing – information received through the senses is ‘processed’ by various systems in the brain. Some systems store the information in the form of memory, and other systems control behaviour. Some systems operate automatically and unconsciously, while others are conscious and require effort on the part of the individual. Because the information-processing approach was first devised to describe the operations of complex physical systems such as computers, the modern model of the human brain is, for most cognitive psychologists, the computer. As you will see in Chapter 7, another model (neural networks) is now being used as an alternative to the computer. Although cognitive psychologists study mental structures and operations, they have not gone back to the introspective methods that structuralists such as Wundt employed. Instead, they use experimental methods, under controlled conditions, to test hypotheses and discover facts about how we think and remember. Cognitive psychologists such as Donald Broadbent, Stanley Schachter, Neal Miller, Don McClelland, Alan Baddeley, Ulric Neisser, Allan Paivio, Stephen Kosslyn, Endel Tulving, Elizabeth Loftus, Daniel Kahneman and Amos Tversky (the last two won the Nobel Prize for economics in 2002) discovered new and important data about how we learn to learn, remember and reason. You’ll find their research in Chapters 8 and 11 but also throughout the book.
Elizabeth Loftus.
Alan Baddeley.
Source: Jodi Hilton/Pool/Reuters
Source: Copyright UK Medical Research Council (2009) used by kind permission.
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Daniel Kahneman.
Amos Tversky.
Source: Corbis: Reuters
Source: Barbara Tversky
The biological revolution Biology has always been closely tied to psychology and as psychology began to flourish, it was against a backdrop of some quite staggering discoveries in the physical science. For example, Descartes’s hydraulic model of muscular movement was shown to be incorrect by Luigi Galvani (1737–98), an Italian physiologist who discovered that muscles could be made to contract by applying an electrical current directly to them or to the nerves that were attached to them. The muscles themselves contained the energy needed for them to contract. They did not have to be inflated by pressurised fluid. This discovery is the source of a modern-day technique for helping people recover from serious, paralysing illnesses and injury: the use of brain electrical activity to control objects such as a computer cursor or a prosthetic limb. There is a special Psychology in Action section on this technique in Chapter 4.
chemicals, and manipulate other conditions in order to see how the organism worked. His most important contribution to what would become the science of
The brain and sensation: Johannes Müller The work of the German physiologist Johannes Müller (1801–58) flags a definite transition from the somewhat sporadic, isolated instances of research into human physiology to the progressively more direct and precise exploration of the human body. Müller was a forceful advocate of applying experimental procedures to the study of physiology. He recommended that biologists should do more than observe and classify; they should remove or isolate animals’ organs, test their responses to
Johannes Müller (1801–58).
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psychology was his doctrine of specific nerve energies. He noted that the basic message sent along all nerves was the same – an electrical impulse. And the impulse itself was the same, regardless of whether the message concerned was, for example, a visual perception or an auditory one. What, then, accounts for the brain’s ability to distinguish different kinds of sensory information? That is, why do we see what our eyes detect, hear what our ears detect, and so on? After all, both the optic nerves and the auditory nerves send the same kind of message to the brain. The answer is that the messages are sent over different channels. Because the optic nerves are attached to the eyes, the brain interprets impulses received from these nerves as visual sensations. You have probably already noticed that rubbing your eyes causes sensations of flashes of light. When you rub your eyes, the pressure against them stimulates visual receptors located inside. As a result of this stimulation, messages are sent through the optic nerves to the brain. The brain interprets these messages as sensations of light. Müller’s ideas have endured, forming the basis for investigations into the functions of the nervous system. For centuries, philosophers had identified thinking or consciousness as the distinguishing feature of the human mind and had concluded that the mind was located in the brain. Now the components of the nervous system were being identified and their means of operation were being explored. Pierre Flourens (1794–1867), a French physiologist, provided experimental evidence for the implications of Müller’s doctrine of specific nerve energies. He operated on animals, removing various parts of the nervous system. He found that the resulting effects depended on which parts were removed. He observed what the animal could no longer do and concluded that the missing capacity must have been the function of the part that he had removed. For example, if an animal could not move its leg after part of its brain was removed, then that region must normally control leg movements. This method of removal of part of the brain, called experimental ablation (from the Latin ablatus, ‘carried away’), was soon adopted by neurologists, and it is still used by scientists today. Through experimental ablation, Flourens claimed to have discovered the regions of the brain that control heart rate and breathing, purposeful movements, and visual and auditory reflexes.
Brain damage and behaviour: Paul Broca and Carl Wernicke One of the first people to apply the logic of Flourens’s method to humans was Paul Broca (1824–80). In 1861, Broca, a French surgeon, reported the results of an
autopsy on the brain of a man who had suffered a stroke several years previously. The stroke (damage to the brain caused, in this case, by a blood clot) had caused the man to lose the ability to speak. The patient, whose real name was Leborgne, was called Tan because this was the only word he uttered. Broca discovered that the stroke had damaged part of the brain on the left side, as Figure 1.5 shows, although Marc Dax had reported similar findings earlier that century. Broca suggested that this region of the brain is a centre for speech – this part is now called Broca’s area. Broca’s work was followed, independently, by Carl Wernicke (1848–1905), who noted that damage to an adjacent part of the brain on the same side impaired his patient’s speech comprehension and production. Chapter 10 has more on both of these language disorders and how psychologists still debate the areas which, if damaged, create problems in speech production and comprehension. Recent research, for example, suggests that the brain also needs to be injured outside Broca’s area in order to see the deficit reported in his patient (Dronkers et al., 2007). Studying the effects of accidental brain damage on function has allowed neuroscientists to predict which regions of the brain may be involved in specific functions. One famous example of brain damage leading to speculation about the function of a brain region is that of Phineas Gage. Gage was a railroad construction supervisor who, in the mid-nineteenth century, had an accident at work. An iron rod shot through his face, through the front part of his brain and straight out of the top of his head. A reconstructed image of the trajectory of the rod through his skull can be seen in Figure 1.6a. Figure 1.6b is the only existing image of Gage (with the rod tastefully superimposed).
Figure 1.5 A photograph of Tan’s brain. Note the egg-shaped cavity – this was thought to be responsible for his inability to speak fluently. Source: T.E. Feinberg and M.J. Farah (1997) Behavioral Neurology and Neuropsychology. © The McGraw-Hill Companies.
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Localisation of function: Gustav Fritsch and Eduard Hitzig, Franz Gall and Johann Spurzheim
(a)
(b) Figure 1.6 On a September afternoon in 1848, an unusual accident befell a young American railroad worker called Phineas Gage. An iron rod shot through his head as a result of an uncontrolled explosion at work. Almost 150 years later, Hannah Damasio and her colleagues at the University of Iowa took the medical reports of Gage’s injury and plotted the course of the rod, using modern computer technology. (a) Shows one of the images of the rod’s trajectory. (b) Shows a depiction of Gage himself. Source: (a) From H. Damasio, T. Grabowski, R. Frank, A.M. Galaburda and A.R. Damasio, The return of Phineas Gage: Clues about the brain from a famous patient. Science, 1994, 264: 1102–05. Department of Neurology and Image Analysis Facility, University of Iowa. (b) From MIT:Bradford Macmillan, An odd kind of fame.
Whereas before the injury, Gage had been a hardworking and conscientious individual, after the injury he became boorish, unpleasant and unreliable. The part of the brain damaged seemed to be that responsible for inhibiting inappropriate behaviour. We now know that patients with damage to this part of the brain have difficulty in inhibiting such behaviour (there is more on this phenomenon in Chapter 13).
In 1870, the German physiologists Gustav Fritsch and Eduard Hitzig introduced the use of electrical stimulation as a tool for mapping the functions of the brain. For example, Fritsch and Hitzig discovered that applying a small electrical shock to different parts of the cerebral cortex caused movements of different parts of the body. In fact, the body appeared to be ‘mapped’ on the surface of the brain, so that the feet, hands, fingers and so on, had a part of the brain dedicated to them. Originally, this work was conducted on dogs on Frau Hitzig’s dressing table (because they had no available laboratory space). Such humble conditions gave rise to the first experiment in localisation of function in the brain – the goal of neuropsychology. No less elaborate, but ultimately doomed, was the attempt at localising function by Franz Gall (1758–1828) and Johann Spurzheim (1776–1832). Their anatomical personology – or as it is commonly known, phrenology – suggested that if we were very adept at a function the part of the brain responsible would be overactive. This overactivity caused an indentation in the skull. If a person was mathematically gifted, therefore, the part responsible for this would be active and cause a bump in the skull, which the experimenter could palpate. This hypothesis was beautifully testable and it was not long before the edifice came crashing down. It is, however, an attempt at localising function in the brain. Although Gall is best known for this, he also made more worthwhile contributions to neuroscience, such as identifying the importance of the left front part of the brain to speech.
Speed and magnitude of nerve impulses: Hermann von Helmholtz and Ernst Weber A different and yet essentially physical approach to studying behaviour was also seen in the work of the German physicist and physiologist Hermann von Helmholtz (1821– 94), who did much to demonstrate that mental phenomena could be explained by physiological means. This extremely productive scientist made contributions to both physics and physiology. He actively disassociated himself from natural philosophy, from which many assumptions about the nature of the mind had been derived. Müller, under whom Helmholtz had conducted his first research, believed that human organs were endowed with a vital immaterial force that coordinated physiological behaviour, a force that was not subject to experimental investigation. Helmholtz would allow no such assumptions about unproved (and unprovable) phenomena. He advocated a purely scientific approach, with conclusions based on objective investigation and precise measurement.
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In Germany, a contemporary of von Helmholtz’s, Ernst Weber (1795–1878), began work that led to the development of a method for measuring the magnitude of human sensations. Weber, an anatomist and physiologist, found that people’s ability to tell the difference between two similar stimuli – such as the brightness of two lights, the heaviness of two objects, or the loudness of two tones – followed orderly laws. This regularity suggested to Weber and his followers that the study of perceptual phenomena could be as scientific as that of physics or biology. In Chapter 6 we consider the study of the relation between the physical characteristics of a stimulus and the perceptions they produce, a field called psychophysics, or the physics of the mind.
Cognitive neuroscience: the future of the biology of the ‘mind’?
Hermann von Helmholtz (1821–94).
Until Helmholtz’s time, scientists believed that the transmission of impulses through nerves was as fast as the speed of electricity in wires; under this assumption, transmission would be virtually instantaneous, considering the small distances that impulses have to travel within the human body. Helmholtz successfully measured the speed of the nerve impulse and found that it was only about 90 feet per second, which is considerably slower than the speed of electricity in wires. This finding suggested to later researchers that the nerve impulse is more complex than a simple electrical current passing through a wire, which is indeed true. Helmholtz also attempted to measure the speed of a person’s reaction to a physical stimulus, but he abandoned this attempt because there was too much variability from person to person. However, this variability interested scientists who followed him; they tried to explain the reason for individual differences in behaviour. Because both the velocity of nerve impulses and a person’s reactions to stimuli could be measured, researchers theorised that mental events themselves could be the subject of scientific investigation. Possibly, if the proper techniques could be developed, one could investigate what went on within the human brain. Thus, Helmholtz’s research was important in setting the stage for the science of psychology.
The cognitive revolution did not lead to a renewed interest in biology. But the extraordinary advances in neurobiology in the late twentieth century have revolutionised psychology. Neurobiologists (biologists who study the nervous system) and scientists and engineers in allied fields have developed ways to study the brain that were unthinkable just a few decades ago. We can study fine details of nerve cells, discover their interconnections, analyse the chemicals they use to communicate with each other, produce drugs that block the action of these chemicals or mimic their effects. More importantly, using PET or (now, more commonly) fMRI, we can see the internal structure of a living human brain, and measure the activity of different processes of the brain – in regions as small as a few cubic millimetres – while people are thinking, feeling, perceiving, comprehending and moving (Martin, 2006; Raichle, 2008). One application of this technique can be seen in Figure 1.7 (a)–(b). This combination of cognitive psychology and neuroscience – cognitive neuroscience – provides a different way of studying behaviour and describing its causes. Currently, the endeavours in cognitive neuroscience are, because of the nature of the techniques used, directed towards studying basic, yet essential, behaviour such as rudimentary reading, recognising emotion, remembering and speaking. But this is changing and studies are now using neuroimaging to study how people converse, make moral decisions, appreciate television programmes, react to a lover’s face and voice and even understand magic tricks. You’ll find a review of many of these studies in Chapter 4.
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Conceptual and historical issues in psychology
(a) Areas where normal readers show more activation than do dyslexic participants.
(b) Areas where dyslexic participants shown more activation than do normal readers. Figure 1.7 Areas of activation in the human brain while it engages in language tasks. In this experiment, the reading performance and brain activation of dyslexic and normal readers are compared. Source: Brunswick, N., McCory, E., Price, C., Frith, C. and Frith, U., Explicit and implicit processing of words and pseudowords by adult developmental dyslexics: A search for Wernicke’s Wortschatz? Brain, 1999, 122, 1901–17. Reproduced with permission from Oxford University Press.
As this chapter has shown you, understanding a discipline’s past can help you better understand its present and its future. Understanding a discipline’s past shows you the stages – usually chaotic, not linear or orderly – that psychology has gone through to reach the status it has attained today and the body of knowledge it has accrued. The shifts in approach and subject matter across its history will be reflected in its future shifts. But these shifts will be gradual. The danger in highlighting stages in history, as is done here, is that that they are seen as discrete and self-contained. They are only discrete and self-contained because the prism of historical retrospection makes them so and we can reflect back, soberly, on some of the momentous conceptual and experimental changes that psychology underwent. We are currently amidst an extraordinary boom in neuroimaging work. In 50 years’ time, all of this work may seem quaintly obsolete. We don’t know. Historical milestones are one thing. Conceptual issues are another. The trends and schools described here arose when researchers operated in a different world and context to that in which we operate today. Much – if not most – research conducted in universities is funded by government, and government has priorities. Will these priorities see a shift in the types of topics psychologists study in the future? On a grander scale, conceptual issues can be virtually synonymous with philosophical issues. For example, the question ‘Is the scientific method the best method for establishing truth?’ is a philosophical, rather than a psychological question, because it doesn’t have an absolute answer. When we have answers to questions, philosophy is dead. In the chapters that follow you should be able to see how the research they describe arose and in what context – how some of the work in social psychology emerged from real-life events, such as the apparent reluctance to assist a person crying for help, or a soldier saying he was only obeying orders, for example. Or how crosscultural research on facial expression led to a theory of emotion. Or how research on race differences in IQ became controversial. Or how we classify and diagnose mental illness. Or how sociobiology, according to some views, reduces human beings to self-interested savages.
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So far, you have seen how psychology is a discipline that comprises a number of different branches. This survey of the history of psychology reveals a number of methodological approaches to the study of behaviour. In
the next chapter you will see in more detail how psychologists study behaviour. You will also discover the dominant methodological approach to answering questions about psychology.
Chapter review – Organisational or occupational psychologists study the behaviour of individuals and groups in the workplace. – Ergonomists help to design machines and workplace environments that enhance work performance.
What is psychology? • Psychology is the science of behaviour, and psychologists study a large variety of behaviours in humans and other animals.
• Psychology has many major branches: – Psychobiologists study the biological basis of behaviour. – Psychophysiologists study people’s physiological reactions, such as changes in heart rate and muscle tension. – Neuropsychologists study the relationship between central nervous system activity and structure and function. – Comparative psychologists study the evolution of behaviour by comparing the behavioural capacities of various species of animals. – Ethologists study the biological bases of behaviour through observation of animals in natural environments. – Sociobiologists attempt to interpret human and animal behaviour in terms of evolution and biological inheritance. – Behaviour geneticists study the degree of influence exerted by heredity and environment on behaviour. – Cognitive psychologists study complex human behaviours such as cognition, memory and attention. – Cognitive neuroscientists study the role of the human and animal brain in behaviour. – Developmental psychologists study the development of behaviour throughout the lifespan. – Social psychologists study the effects of people on the behaviour of other people. – Individual differences involves the study of the effects of specific characteristics or traits on behaviour. – Cross-cultural psychologists study the impact of culture on behaviour. – Forensic and criminological psychologists study the ways in which psychological knowledge can be applied in criminal and legal settings. – Clinical psychologists study the causes and treatment of mental disorders and problems of adjustment. – Health psychologists study the ways in which lifestyle and behaviour affect illness and health. – Educational psychologists assess the cognitive, social and emotional development of children in the school environment. – Consumer psychologists study what motivates people to consume and how consumers’ perceptions are formed.
The development of psychology as a science • Psychology has its modern roots in the thinking of the French philosopher and mathematician René Descartes who argued that the mind and the body were two separate entities which interacted (dualism). • The mid-nineteenth century gave rise to materialism and empiricism. Materialism maintained that the mind was made of matter; thus all natural phenomena, including human behaviour, could be explained in terms of physical entities: the interaction of matter and energy. Empiricism emphasised that all knowledge was acquired by means of sensory experience; no knowledge was innate. The concept of empiricism was developed by the philosophers John Locke and David Hume.
Modern psychology • The first laboratory of experimental psychology was established in Leipzig in 1879 by Wilhelm Wundt.
• Wundt and his colleagues’ work gave rise to structuralism: the idea
• •
•
•
•
that the mind was made up of components which could be broken apart and studied. The method of studying these components was introspection – the observation and recall of experience. At about the same time, Ebbinghaus contributed important methods for objectively measuring learning and forgetting. Darwin’s ground-breaking theory of evolution, or theory of natural selection, argued that traits necessary for survival would be inherited and that only those adaptively useful traits would survive. Francis Galton founded the scientific study of individual differences in human behaviour and suggested that certain psychological characteristics could be inherited. Functionalism, which grew out of Darwin’s theory of evolution, was concerned with the processes of consciousness such as perceiving and learning. Its major advocates were William James and James Angell. Functionalism gave rise to behaviourism, founded by John Watson, which still dominates the way we do research. The
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subject matter of behaviourism is observable behaviour; according to the behaviourists, mental events – because they were unobservable – should play no part in scientific psychology. Behaviourism developed a radical strain in the 1950s which viewed the organism’s behaviour strictly in terms of stimulus and response. • Humanistic psychology is concerned with the special nature of humanity and emphasises human experience, choice and creativity, and the potential for personal growth. • The cognitive revolution arose from the belief that behaviourism’s emphasis on observable behaviour missed some of the complexity of human cognition and behaviour. The cognitive
revolution saw a rekindling of interest in phenomena such as memory, thinking, creativity, imagination and so on, and human behaviour was interpreted in terms of information processing. • The biological revolution in psychology manifested itself in the increased interest of psychologists in all fields – not just physiological psychology – in the role of biological factors in behaviour. This has given rise to cognitive neuroscience in which the disciplines of neuropsychology and cognitive psychology have combined and used neuroimaging methods to create a greater understanding of the role of the brain in thinking, feeling and perceiving, specifically to localise function in the brain.
Suggestions for further reading The history of psychology Crivellato, E. and Ribatti, D. (2007) Soul, mind, brain: Greek philosophy and the birth of neuroscience. Brain Research Bulletin, 71, 327–36. Hock, R. (2009) Forty studies that changed psychology (6th edn). Harlow: Pearson Education. Leahey, T.H. (2003) A History of Psychology (6th edn). Englewood Cliffs, NJ: Prentice Hall International. Mandler, G. (2002) Origins of the cognitive (r)evolution. Journal of History of the Behavioral Sciences, 38, 4, 339–53. Shepard, R.N. (2004) How a cognitive psychologist came to seek universal laws. Psychonomic Bulletin and Review, 11, 1, 1–23. Several sources describe the history of psychology, including its philosophical and biological roots, and these are some very good introductions.
Concepts and controversies in psychology Furnham, A. (1996) All in the Mind. London: Whurr Publishers. Kassin, S., Briggs, K.H. and Tavris, C. (2008) Current Directions in Introductory Psychology. Boston: Allyn & Bacon. Valentine, E.R. (1992) Conceptual Issues in Psychology (2nd edn). London: Routledge. Excellent introductions to some of the controversial issues and the major concepts in psychology.
Influential psychologists Cohen, D. (2004) Psychologists on Psychology. London: Hodder & Stoughton.
Fancher, R.E. (1996) Pioneers of Psychology (3rd edn). New York: W.W. Norton. Kimble, G.A., Wertheimer, M. and White, C.L. (1991) Portraits of Pioneers in Psychology. Hillsdale, NJ: Lawrence Erlbaum Associates/American Psychological Association. Cohen’s book contains an excellent set of interviews with some of the leading psychologists of the time. The books by Kimble et al. and Fancher contain biographical sketches of the major scientists who have contributed to psychology and so provide a good potted introduction to the personalities (and themes, ideas and developments) in psychology.
Reflections on psychology’s past and future Fuller, R., Walsh, P.N. and McGinley, P. (1997) A Century of Psychology. London: Routledge. Solso, R.L. (1997) Mind and Brain Sciences in the 21st Century. Cambridge, MA: MIT Press. British Journal of Psychology, special issue, Supplement 1, April 2009. The two books comprise a collection of chapters written by some of the last century’s outstanding psychologists. Both are good books to read if you are interested in the leading scientists’ assessment of psychology’s past and their predictions of how psychology will develop in the future. The special issue of the British Journal of Psychology reprints some of the most influential research papers of the past 100 years, with commentaries.
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Journals to consult American Psychologist
European Psychologist
Annual Review of Psychology
Psychological Bulletin
Australian Psychologist
Psychological Science
British Journal of Psychology
The Psychologist
Current Directions in Psychological Science
Website addresses General psychology
http://psychclassics.asu.edu/Titchener/structuralism.htm
http://www.utoledo.edu/~mcaruso/prolynxnf.html A massive collection of links to psychology and education-related websites.
http://psychclassics.asu.edu/Titchener/strucfunc.htm Titchener’s views on structuralism and functionalism, from Philosophical Review (1898).
http://www.tamiu.edu/coah/psy/directories.htm A collection of psychological resources web pages. http://onlinebooks.library.upenn.edu/webbin/book/subjectstart?BF This is a link to the University of Pennsylvania’s collection of online psychology texts. It is frighteningly sub-headed ‘Psychology (include. Parapsychology and the occult)’ but don’t let this put you off. www.improb.com A sceptical treatment of the eccentricities in science, including psychology, from the authors and editors of the Annals of Improbable Research. http://www.psychology.org/links/Resources/Pseudoscience/ A collection of sites critical of pseudoscience. http://nobelprize.org/nobel_prizes/economics/laureates/2002/ kahneman-lecture.html An online video of Daniel Kahneman’s Nobel Prize lecture. http://www3.uakron.edu/ahap/ The Archives of the History of American Psychology– some interesting video and audio clips in here. http://www.muskingum.edu/~psych/psycweb/history.htm A collection of biographies of well-known historical figures in psychology.
From the archive This is a selective list of some of the outstanding contributions to psychological thinking made by some significant philosophers and psychologists over the centuries. They are available free and online. The psychclassics site has been developed by Christopher Green. http://psychclassics.asu.edu/Aristotle/De-anima/index.htm Aristotle’s De Anima, 350 BC. http://psychclassics.asu.edu/Berkeley/vision.htm Berkeley’s An essay towards a new theory of vision, 1732 (4th edn). http://psychclassics.asu.edu/Wundt/Physio/ Wundt’s Principles of Physiological Psychology (1874/1902/1904).
http://psychclassics.asu.edu/Titchener/brentano-wundt.htm Titchener’s article on Brentano and Wundt from American Journal of Psychology (1921). http://psychclassics.asu.edu/Angell/functional.htm James Angell’s ‘The province of functional psychology’ from Psychological Review (1907). http://psychclassics.asu.edu/Allport/frame.htm Gordon Allport’s ‘The psychologist’s frame of reference’ in Psychological Bulletin (1940). http://psychclassics.asu.edu/Pavlov/ Pavlov’s Conditioned reflexes: An investigation of the physiological activity of the cerebral cortex (1927). http://psychclassics.asu.edu/Watson/views.htm Watson’s ‘Psychology as the behaviourist views it’, from Psychological Review (1913). http://psychclassics.asu.edu/Titchener/watson.htm Titchener’s comments on above (1914) from Proceedings of the American Philosophical Society. http://psychclassics.asu.edu/Watson/emotion.htm Watson and Rayner’s ‘Conditioned emotional reactions’ from Journal of Experimental Psychology (1920). http://psychclassics.asu.edu/Jones/ Jones’s ‘A laboratory study of fear: the case of Peter’ from Pedagogical Seminary (1924). http://psychclassics.asu.edu/Watson/Battle/ Two papers by Watson and MacDougall on behaviorism (1929). http://psychclassics.asu.edu/Tolman/formula.htm Tolman’s ‘A new formula for behaviorism’ from Psychological Review (1922). http://psychclassics.asu.edu/Tolman/Maps/maps.htm Tolman’s ‘Cognitive maps in rats and men’ from Psychological Review (1948).
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http://psychclassics.asu.edu/Hull/Hierarchy/part1.htm http://psychclassics.asu.edu/Hull/Hierarchy/part2.htm Hull’s concept of the habit–family hierarchy and maze learning from Psychological Review (1934). http://psychclassics.asu.edu/Skinner/Twotypes/twotypes.htm http://psychclassics.asu.edu/Skinner/Konorski/ http://psychclassics.asu.edu/Skinner/ReplytoK/reply.htm Two papers by Skinner on the conditioned reflex from Journal of General Psychology (1935), plus a reply. http://psychclassics.asu.edu/Skinner/Pigeon/ Skinner’s ‘superstition’ in the pigeon article from Journal of Experimental Psychology (1948).
http://psychclassics.asu.edu/Skinner/Theories/ Skinner’s ‘Are theories of learning necessary?’ from Psychological Review (1950). http://psychclassics.asu.edu/Ebbinghaus/index.htm Ebbinghaus’s Memory: A contribution to experimental psychology (1885). http://psychclassics.asu.edu/Munster/Witness/ Munsterberg’s On the witness stand (1908/1925). http://psychclassics.asu.edu/Terman/terman1.htm Terman’s chapter ‘The uses of intelligence tests’ (1916). http://psychclassics.asu.edu/Galton/talent.htm Galton’s ‘Hereditary talent and character’ from Macmillan’s Magazine (1865).
Addresses Major international professional psychology organisations and societies Europe
Cyprus
European Federation of Psychologists’ Associations http://www.efpa.be
Cyprus Psychologists’ Association, PO Box 20537, CY-1678 Nicosia, Cyprus
Australia
Czech Republic
Australian Psychological Society, PO Box 38, Flinders Lane Post Office, Melbourne VIC 8009 http://www.psychology.org.au/
Unie Psychologickych Asociaci CR, Kladenska 48, CR-16000 Praha 6, Czech Republic
Denmark Austria Berufsverband Österreichischer, Psychologen/innen, Möllwaldplatz 4/4/39, A-1040 Vienna, Austria http://www.boep.or.at
Belgium Belgische Federatie van Psychologen-Fédération Belge des Psychologues BFP, Agora galerij, Grasmarkt 105/18, B-1000 Brussels, Belgium http://www.vub.ac.be/gst/bfp
Canada Canadian Psychological Association, 141 Laurier Avenue West, Suite 702, Ottawa, Ontario K1P 5J3 http://www.cpa.ca/cpasite/splash.asp
Croatia Croatian Psychological Association, Ivana Lucica 3, HR-10000 Zagreb, Republic of Croatia
Dansk Psykologforening, Stockholmsgade 27, DK-2100 Kobenhavn, Denmark
Estonia Eesti psühholoogide liit – Union of Estonian Psychologists, c/o Toomas Niit, Department of Psychology, Tallinn Pedagogical University, PO Box 572, EE-0010 Tallinn, Estonia
Finland Suomen Psykologiliitto, Bulevardi 30 B3, 00120 Helsinki, Finland http://www.psyli.fi
France Association Nationale des Organisations de Psychologues – ANOP, 20 bis Grand Rue, Croix Rouge, F-13013 Marseille, France http://www.club-internet.fr/perso/anop
Germany Berufsverband Deutscher Psychologinnen und Psychologen e.V. – BDP, Glinkastrasse 5–7, D-10117, Berlin, Germany http://www.bdp-verband.org
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Greece
Norway
Association of Greek Psychologists, Avlidos 8, 11527 Athens, Greece
Norsk Psykologforening (Norwegian Psychological Association), Norsk Psykologforening Postboks 8733 Youngstorget, N-0028 Oslo, Norway http://www.psykol.no
Hungary Magyar Pszichológiai Társaság, PO Box 220, H-1536 Budapest, Hungary
Poland
Iceland
Polskie Towarzystwo Psychologow Praktykow (Polish Society of Professional Psychologists), ul. Koszykarska 33, 30717 Krakow, Poland
Association of Icelandic Psychology, Lagmuli 7, IS’-108, Reykjavik, Iceland
Ireland Psychological Society of Ireland, CX House, 2a com Exchange Place, Poolbegstreet, IRL-Dublin 2, Ireland
Italy Italian Network of Professional Psychologists Association, c/o AUPI, Via Arenula 16, 00186 Roma, Italy http://www.aupit.it
Latvia Latvijas Profesionalo Psihologu Asociacija, Latvijas Universitate, abon. kaste 238, LV 1011 Riga, Latvija
Liechtenstein
Portugal Sindicato Nacinal dos Psicologos, R. Ferreira Lapa 2-B, 3- Dto., P1150-157 Lisbon, Portugal
Slovakia Slovenska komora psychologov, Zapadna 2, 82102 Bratislava, Slovakia
Slovenia Drustvo Psihologov Slovenije, Ulica stare pravde 2, SLO-1000 Ljubljana, Slovenia
Spain Colegio Oficial de Psicologos, C/Conde de Peñalver, num. 45-5°, E-28006 Madrid, Spain
Berufsverein der Psychologen/innen Liechtensteins, Meierhofstrasse 100, FL-9495 Triesen, Liechtenstein
Sweden
Lithuania
Sveriges Psykologforbund, Box 3287, S-10365 Stockholm, Sweden http://www.psykologforbundet.se
Lithuanian Psychological Association, Didlaukio 47, Vilnius 2057, Lithuania
Luxembourg Société Luxembourgeoise de Psychologie, BP 1787, L-1017 Luxembourg, Luxembourg http://www.slp.lu
Malta Malta Union of Professional Psychologists, PO Box 341, Valletta, Malta
The Netherlands Nederlands Instituut van Psychologen, Postbus 9921, 1006 AP Amsterdam, The Netherlands http://www.psynip.nl
Switzerland Foderation der Schweizer Psychologinnen und Psychologen FSP, Choisystrasse 11, 3000 Bern 14, Switzerland http://www.fsp.psy.ch
Turkey Turkish Psychological Association, P.K., Mesrutiyet Cad. 22/12 Kizilay, 06640, Ankara, Turkey
United Kingdom The British Psychological Society, St Andrews House, 48 Princess Road East, Leicester LE1 7DR http://www.bps.org.uk
United States of America American Psychological Association, 750 First Street, NE, Washington, DC 20002-4242 http://www.apa.org
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Research methods in psychology
Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activities on: Distinguishing independent and dependent variables • Personality testing • Ethics in Psychological Research • Descriptive statistics, finding the average • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
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Clever Hans: A lesson in research methods Because of his long-lasting fame at the turn of the century many people know about ‘Clever Hans’, the mindreading horse. If people gave the owner a question for Hans, he would look directly at the horse and repeat the question in what seemed like a normal tone of voice. Hans would then lift his hoof and tap out the answer. Thus, if asked, ‘What is 2 + 2?’, Hans would tap the ground four times. After Hans had given the correct answer, the owner would reward the animal by patting it or give it food as a reward. In 1904, several of the best-known scientists in Germany formed a ‘commission’ to study the animal. These distinguished scientists stated boldly that they could find no evidence that Hans was responding to external cues from his questioners and perhaps really could read minds. However, the psychologist on the commission, clearly not satisfied, told one of his graduate students to look into the matter. The student put blinkers on Hans so the animal could not watch the people who were asking him the questions. The horse’s ability to respond correctly decreased significantly. Clever Hans was, indeed, a ‘genius of a horse’ but was not a mind-reader. The animal was superb at reading ‘body language’ – cues that questioners almost always give to an animal. But these were so slight and so subtle that most people were completely unaware they were giving them. In this sense, the sceptics
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were right all along. Source: Furnham, 1996, pp. 83–5.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 2
• Define and describe the scientific approach to studying psychological variables.
• Describe the quantitative and qualitative approaches to psychology and be aware of the advantages and disadvantages of each.
• Define concepts such as hypotheses, theories and variables. • Have an awareness of how psychologists control variables. • Have an awareness of the ethical principles adopted by psychologists.
QUESTIONS TO THINK ABOUT
• What is the scientific method and why is it so important to psychology?
• What are the goals of psychological research? • Does following the steps of the scientific method guarantee that the results of a study will be important?
• Does the scientific method apply to all psychological research?
• How would you set up experiments to answer some of the questions you have about behaviour?
• How do the methods of psychology differ from those of other sciences? Do they?
• Why is obtaining informed consent from participants who take part in research important?
• Are some psychological subjects impossible to study? Why? • What are the dangers in drawing conclusions from studies in which there is only one participant?
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The process of discovery in psychology: the scientific method The goal of psychological research is to discover, describe, explain and change the causes of behaviour. To do this, we need to describe behaviours and the events that are responsible for their occurrence in a language that is both precise enough to be understood by others and general enough to apply to a wide variety of situations. As you saw in Chapter 1, this language takes the form of explanations, which are general statements about the events that cause phenomena to occur. The nature of these general statements will become clear as we see how psychologists use the scientific method. There are three major scientific approaches to research. Naturalistic observations – observations of people or animals in their natural environment – are the least formal and are constrained by the fewest rules. Naturalistic observations provide the foundations of the biological and social sciences. As Chapter 3 shows in detail, Charles Darwin’s observation and classification of animals, plants and fossils during his voyage around the world provided him with the raw material for his theory of evolution. Jean Piaget collected much of his early data by observing his own children. Correlational studies are observational in nature, but they involve more formal measurement – of environmental events, of individuals’ physical and social characteristics, and of their behaviour. Researchers examine the relations between these measurements in an attempt to discover the causes of the observed behaviours. Experiments go beyond mere measurement. A psychologist performing an experiment makes things happen and observes the results. As you will see, only an experiment can positively identify cause-and-effect relations. The scientific method consists of a set of rules that dictates the general procedure a scientist must follow in their research. These rules are not arbitrary; they are based on logic. The following five steps summarise the rules of the scientific method that apply to experiments, the most rigorous form of scientific research. As we will see later, many of these rules also apply to observational studies. Some new terms introduced here without definition will be described in detail later in this chapter.
Stages in experimentation
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1 Identify the problem and formulate hypothetical causeand-effect relations among variables. This step activit ee involves identifying variables (particular behaviours and environmental and physiological events) yp sych and describing the relations among them in gen-
eral terms. Consider the hypothesis that positive mood increases creativity. This statement describes a relation between two variables – mood and creativity – and states that an increase in one causes an increase in the other.
2 Design the experiment. Experiments involve the manipulation of factors called independent variables and the observation of dependent variables (these are defined in detail later in the chapter). For example, if we wanted to test the hypothesis that positive mood (independent variable) increases creativity (dependent variable), each variable would have to be operationally defined. The independent variable must be controlled so that only it, and no other variable, is responsible for any changes in the dependent variable. 3 Conduct the experiment. The researcher must organise the material needed to perform the experiment, train the people who will conduct the research, recruit volunteers whose behaviour will be observed, assign each of these volunteers to a treatment group or a control group and arrange the setting for the experiment. The experiment is performed and the observations are recorded. 4 Evaluate the hypothesis by examining the data from the study. Do the results support the hypothesis, or do they suggest that it is wrong? This step often involves mathematical procedures used to determine whether the relationship between two variables is statistically significant, i.e. not due to chance. 5 Communicate the results. (See next section.) Following these simple steps decreases the chances that we will be misled by our observations and come to incorrect conclusions from our research. The approach of formulating hypotheses and then setting up experiments to test them is sometimes known as hypothetico-deductive. As you saw in Chapter 1, and will see in Chapter 11, people have a tendency to accept some types of evidence even though the rules of logic indicate that they should not. The Cutting Edge box illustrates this, using a new study of the predictors of having the hepatitis B vaccine. This tendency usually serves us well in our daily lives, but it can lead us to draw the wrong conclusions when we try to understand the true causes of natural phenomena, including our own behaviour (the same tendency results in the making of common-sense mistakes when predicting the outcome of psychological research, as you saw in Chapter 1).
Communicating the results of scientific research Once psychologists have learned something about the causes of a behaviour from an experiment or observational study, they must tell others about their findings. When a piece of research is complete, it is written up in
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Cutting edge – Stories conquer statistics Psychology, like all sciences, uses statistics to determine whether the results it finds are not due to chance. However, humans are less likely to believe statistics than they are convincing narratives: we find words more persuasive. There may be no evidence for a therapy working but a friend’s positive experience of it may convince you to give it a go; there may be no statistical evidence that a multiple vaccination can cause autism, but parents will refuse to allow their children to become so vaccinated because of harrowing case studies allegedly demonstrating this link. Chapter 15 describes a few more of these errors in reasoning.
the form of a journal paper and sent to an academic, peer-reviewed scientific journal. This means that the paper will be critically evaluated, usually anonymously, by two or three of the author’s peers (the process is called ‘peer review’). The editor and reviewer will be individuals with expertise in the author’s field. The scientific method insists that scientists report the details of their research so that other investigators can repeat, or replicate, the study. Replication is one of the great strengths of science; it ensures that erroneous results and incorrect conclusions are weeded out. When scientists publish a study, they know that if the findings are important enough, their colleagues will try to replicate it (perhaps with some variation) to be sure that the results were not just a statistical fluke, specific to the sample studied or the methods used, or the result of some unsuspected errors in the design or execution of the study. The types of article that scientists will write fall broadly into four categories. First, there are empirical papers that report the conduct and results of an experiment. Most scientific journals publish papers of this kind (such as Nature, Psychological Science, British Journal of Psychology, etc.) and most follow a format. They will invariably comprise sections and these sections will include a title, an abstract, an introduction, the method, the results, a discussion, references and an appendix. There are deviations from this format: Science and the Journal of Cognitive Neuroscience, to name only two, do not adopt this structure (the study’s methods are reported either at the end of the paper or on the journal’s website). But, by and large, papers follow this structure:
• Title (and affiliations). The title describes the general thrust of the article. It is normally followed by the full names of all authors together with their affiliation (who they work for/on behalf of, e.g., ‘Department of Psychology, Middlesex University, UK’).
A study in Health Psychology has extended this phenomenon to the area of ill-health prevention (DeWit et al., 2008). An online study examined the effects of narrative evidence and statistical evidence on men’s perception of risk of contracting the hepatitis B virus and whether they would seek vaccination. All the participants were homosexual. As predicted, narrative evidence was more persuasive than statistical evidence in heightening awareness of the risk of contracting the illness and in predicting participants’ intention to get vaccination.
• Abstract. This is usually a 150–200 word paragraph that summarises (‘abstracts’ the information from) the article. It has a statement of intent, a brief description of the study and results and a general conclusion. Some abstracts have a different format and are sectioned in the same way as the paper: research suggests that this is a more informative way of summarising a paper. • Introduction. This is the first of the four major sections of a paper. It reviews the literature pertaining to the subject of the paper and presents a set of hypotheses which the study aims to test. • Method. This section describes what the experimenters did and who took part. Conventionally, this is divided into these subsections: participants, apparatus/materials and procedure. Under participants, all of the important information about the study’s sample is included: age, sex, race, education and any other variable that the study is interested in. The apparatus/ materials section includes details of any specialist technology or materials used. The procedure section describes what the experimenters did. Anyone reading this section should be able to conduct an identical experiment – facilities and time willing – on the basis of reading this section. • Results. This section reports the results of the study. At this stage of your degree, reading the results section of a paper can seem like reading a foreign language because it is replete with impenetrable statistics. • Discussion. The final major section, the discussion, discusses the results found and their implications for the field. If interprets findings in light of previously published data and suggests future avenues of enquiry. • References. This section lists, usually in alphabetical order, all the studies cited in the text. Any study cited in the text should appear here and every item in the reference list should have been cited.
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• Appendix (optional). Sometimes papers include appendices providing additional information such as word lists or questionnaires. Secondly, in addition to journals that publish the results of experiments, there are also those that publish methodological papers reporting a new technique, questionnaire, procedure or new piece of equipment for use in psychological research. Thirdly, there are journals for theoretical papers that formulate a new theory arising from reviewed data. The journal Psychological Review is devoted to articles of this kind, for example. Finally, there are review papers that synthesise a number of articles on a given topic. Psychological Bulletin and Current Direction in Psychological Science publish papers exclusively of this
kind and are good journals for keeping abreast of general topics in psychology. Most journals in psychology, however, tend to focus on the sub-areas of psychology. The European Journal of Social Psychology, Memory and Cognition, Journal of Applied Psychology, Neuropsychologia, Child Development, Personality and Individual Differences, Health Psychology, Emotion, and so on, are examples of this kind. Some journals publish even more specialised research (e.g. Social Neuroscience, Laterality). Researchers also present their findings at conferences or professional conventions. As a result of their research being disseminated, other psychologists can incorporate these findings in their own thinking and hypothesising.
Controversies in Psychological Science – Psychology and the media The issue The media are voracious beasts. Newspapers, television, radio and online sites all have space and air to fill, often with few resources. Psychology’s asset, but also its Achilles heel, is that it studies a topic that most people think they know something about (human behaviour) and produces data that are fascinating and stimulate human interest. The BPS’s Press Office has a media database of over 1,000 members, and receives around 350 queries a month. But how accurately is psychological and other research presented in the media and is this portrayal – skewed or otherwise – important?
The evidence First, let’s start with the source of the research. Simply because a paper is published in a science journal does not mean that its method or results are unassailable. At the extreme end, journals can publish data that turn out to be fraudulent. In 2005, the journal Nature found that 0.3 per cent of the 3,247 scientists who participated in their confidential study claimed to have published bogus data and 6 per cent admitted failing to publish data that contradicted their own theoretical positions. In the same year, Science, one of the two premier general science journals in the world, withdrew a paper by the Korean scientist Hwang Wo-suk because the stem cell lines he had created (and wrote about in Science) did not exist. Another scandal broke in 2004 when the Journal of Reproductive Medicine published a physics-defying article on the effect of prayer on in vitro fertilisation which was generally agreed to be flawed and possibly fabricated. The author was later convicted of criminal fraud. In 2009, an anaesthesiologist was found to have made up most of the data in his 10-year publishing career, and, at the time of writing, editors
are being requested to withdraw 21 of his papers. This man researched the nature of pain management after operations – it was not a frivolous topic of little consequence. Even more seriously, flawed research claiming a link between the MMR vaccine and autism – and, more importantly, the enormously tendentious publicity this generated in 2002–3 – has caused completely avoidable harm to children, given the dramatic increase in measles and mumps following this hoo-hah. Psychology is not immune. There continues to be debate over whether the British psychologist, Cyril Burt, invented his data concerning twins and intelligence. And, of course, there is the famous Sokal Hoax, in which a scientist submitted an utterly nonsensical anti-science article to a famously antiobjectivity social science journal and not only had it accepted but praised by the organ’s clueless reviewers. In experiments to examine whether the peer-review process works, researchers found that there is large variation in what reviewers judge to be quality research – reviewers can normally agree on the really bad studies, but there is more disagreement about the average-to-good ones. Science progresses by contradiction, and new articles develop ideas generated by previous publications or take into account variables that the previous studies had not. Although there are checks in place to weed out ‘bad’ research, it is common to see a lot of it published. This is why you should adopt an inquisitive but informed approach when reading research papers: do not be afraid to question an aspect of procedure or an analysis of logical thinking if you think it is wrong or misguided. You might be right. While some of the stories you see reported or hear broadcast are well researched, balanced and informed it is generally the case that most are not. Journals are intended primarily for other scientists. Journals, however, are also consulted by medical or
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Controversies in Psychological Science – Continued science (or non-specialist) journalists interested in writing about innovative psychological breakthroughs. Conferences at which psychologists present the results of their studies are also extensively reported by specialist reporters in the media and some psychological societies have effective press offices which proactively publicise society conference papers. However, never take any report you read in a newspaper or magazine or see or hear on the television or radio of a published study at face value. If you read the articles on the excellent website www.badscience.net, you will see why: journalists sometimes try to make a study more exciting than it is and make wild claims about the results that the researchers would never dream of doing. According to Goldacre (2008), ‘Science stories generally fall into one of three categories: the wacky stories, the “breakthrough” stories, and the scare stories. Each undermines and distorts science in its own idiosyncratic way’ (p. 208). Stories with headlines such as – and these are genuine – ‘Infidelity is genetic’, ‘Electricity allergy real’, ‘Scans that spot killer babies’ and ‘In future, all men will have big willies’ reflect a tenous relationship with the data (if the data exist) they claim to report. Similarly, newspaper articles claiming to report the mathematical formula for (and, again, all of these are real) the perfect way to eat ice cream (A⫻Tp⫻Tm/Pt⫻At+V⫻LT⫻SP⫻W/Tt=3d20, if you’re interested), the best sitcom, the best way to boil an egg, the best joke, the most depressing day of the year, are all bogus – they are not based on any real research or any real science. Most are commissioned by companies keen to harness the solid appeal of science to market their products. The journalist Nick Davies, in his book Flat Earth News, describes the stories that boast none of the good features of journalism as ‘churnalism’: the writers parrot what is given to them by PR agencies or wire services, often unedited (Davies, 2008). In one survey, 80 per cent of British broadsheet news stories were ‘wholly, mainly or partially’ based on ‘material provided by news agencies and the PR industry’. This is not a trivial issue because most of us will have our first encounter with new studies, not from a studious acquaintance with Web of Knowledge or Science Direct, but from magazines, newspapers, television or radio. We rely on journalists – the conduit between us and the research – to present findings lucidly, accurately, interestingly and not to oversimplify the data or
Identifying the problem: getting an idea for research According to Bausell (1993), psychologists undertake research for a wide variety of reasons – some sensible, some impracticable. Some of these include:
misrepresent it. And the media has influence, through selecting what it exposes. After Kylie Minogue’s well-documented cancer, the Medical Journal of Australia reported a 40 per cent increase in mammogram bookings; in 2009, in the UK, stories reporting the terminal cancer of a female reality TV contestant appeared to coincide with an increase in cervical cancer checks. More self-servingly, the American Association for the Advancement of Science found that a mention of a researcher’s study in the New York Times increased the number of times his or her paper was referred to by other colleagues in their papers (this is an important indicator of impact in the science world). Television and radio exposure increased this still further. One new field that gets both journalists and readers excited is neuroimaging. And the fact that you can illustrate a story involving the brain’s role in behaviour with a screen- and printfriendly brain scan makes the research even more appealing. But neuroimaging technology, and its data analysis, are complex and the studies using it very detailed in their method. Sometimes the details are sacrificed for a headline. Hence, stories screaming: ‘Scary or sensational? A machine that can look into the mind’ (genuine). Chapter 4 will take a further look at the role of brain scans and the way in which they make research more persuasive than a story with just words. In rare circumstances, the authors (researchers and journalists) can collude. An excellent example of this was the so-called study reported in December 2005 – 2005 was clearly a good year for hoaxes – claiming that the success of Agatha Christie was attributable to her use of words and phrases that raised levels of chemicals in the brain (‘Agatha Christie grey cells mystery’ teased The Sunday Times). You would have thought that this study involved neuroimaging or analysis of readers’ brains. In fact, no. You would be hard pushed to find any brain research at all. The study – actually, an examination of the types of words used in Christie’s novels – was used to publicise a television documentary on Christie’s success. The only reference to brain activity in that programme came from a hypnotist and a self-help guru.
Conclusion The important message of this story, and this section, is less complex than a Christie plot but as easy to understand as her prose: question everything.
• changing distasteful professional practice; • • • •
learning everything there is to know about a subject; discrediting a theory that is archaic or wrong; testing a theory to see if it is valid; lending credence to the experimenter’s own theory;
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• • • • • •
furthering a career by producing a seminal study; furthering a career by obtaining a publication; obtaining a doctorate for professional gain; becoming famous; furthering scientific progress; discovering something of intellectual interest.
Which of these do you think makes the best, most realistic goal? Although scientists may undertake study for some or all of these reasons, it is unlikely that they will become famous through their scientific work. Very few scientists attract the fame (and pay) of members from more alluring professions. There are millionaires in psychology, but more in pop music. Publishing a paper for personal gain is also a poor reason. Perhaps the two most important spurs to scientific research are the desires to further science and, more importantly, to discover something of intellectual interest. What do you need to become a good scientist? A great scientist certainly needs to be curious, hard working and dedicated – perhaps even obstinate and relentless. They need to be sceptical, open-minded and methodical. But above all, a successful scientist needs to have good ideas. Where do those ideas come from?
Constructing a hypothesis A hypothesis is the starting point of any study. It is an idea, phrased as a general statement, that a scientist wishes to test through scientific research. In the original Greek, hypothesis means ‘suggestion’, and the word still conveys the same meaning. When scientists form a hypothesis, they are simply suggesting that a relation exists among various phenomena (like the one that might exist between increased positive mood and increased risktaking). Thus, a hypothesis is a tentative statement about a cause-and-effect relation between two or more events. Productive and creative scientists formulate new hypotheses by thinking about the implications of studies that they have performed or that have been performed by others. At other times, however, researchers may not know exactly what they expect to find. Such research endeavours are called ‘fishing expeditions’. In the same way that an angler may not know whether they will catch a trout or an old car seat, the researcher does not know whether they will find result X or result Y. An example of such research would be the measurement of people’s attitudes towards a particular subject such as animal experimentation or alternative medicine. In such cases, an experimenter would not be able to make an absolute prediction based on hypothetico-deductive reasoning (unless, for example, they compared attitudes among two groups such as vegans and meat-eaters, or users of conventional medicine and users of homoeopathic remedies).
Creating a theory A theory, a set of statements designed to explain a set of phenomena, is an elaborate form of hypothesis. In fact, a theory can be a way of organising a system of related hypotheses to explain some larger aspect of nature. A good theory fuels the creation of new hypotheses. More accurately, a good scientist, contemplating a good theory, thinks of more good hypotheses to test. For example, Albert Einstein’s theory of relativity states that time, matter and energy are interdependent. Changes in any one will produce changes in the others. The hypotheses suggested by this theory revolutionised science; the field of nuclear physics rests largely on experiments arising from Einstein’s theory. A good theory is one that generates testable hypotheses – hypotheses that can potentially be supported or proved wrong by scientific research. Some theories are so general or so abstract that they do not produce testable hypotheses and hence cannot be subjected to scientific rigour. The framework for most psychological research is larger in scope than a hypothesis but smaller in scope than a fullyfledged theory. For example, the frustration–aggression hypothesis in social psychology suggests that people (or other animals) tend to become aggressive when they do not achieve a goal that they have been accustomed to achieving. This hypothesis makes a prediction that might fit many different situations. Indeed, many experiments have been performed to test this hypothesis under different conditions. Even though the frameworks that most psychologists construct fall short of constituting theories, they serve a similar function by stimulating researchers to think about old problems in new ways and by showing how findings that did not appear to be related to each other can be explained by a single concept. One recent theory of emotional experience, for example, suggests that increases or decreases in the left and right front part of the brain are associated with positive and negative emotions, reflecting a tendency to ‘withdraw’ or ‘approach’ a stimulus (Davidson and Sutton, 1995). Such a theory can be used to test a number of hypotheses such as, ‘depressed individuals will show less left frontal brain activity’ and research on frontal lobe activation and emotion has resulted in a modification of thinking on the relationship between the two (Peters and Harmon-Jones, 2009), as you’ll see in Chapter 13.
Quantitative research methods: designing an experiment Although naturalistic observations enable a psychologist to classify behaviours into categories and provide hypothetical explanations for these behaviours, only an
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experiment can determine whether these explanations are correct. This approach is known as quantitative research because behaviours are reduced to quantities or can at least be seen as quantifiable. Personality or visuospatial ability may be quantified by a score on a questionnaire, for example, or the ability to react correctly and quickly on a reaction time task may be quantified by the number of correct decisions and the speed of responding. There are various types of experiment we can design. We could conduct an experiment in which we looked at the effect of sleep deprivation on mental arithmetic ability; one group might be deprived of sleep for 24 hours, another for 36 hours and another would be allowed to sleep normally. In a more elaborate study, we could use neuroimaging techniques to monitor changes in brain activation at each stage. In the neuroimaging study this would be the control group because it is unafactivit ee fected by the features of the experiment that we are interested in looking at and can, therefore, yp sych be used as a comparison group. The others are called experimental groups. Because the individuals in one group are not the same people as the ones in another group, the design of the experiment is called independent groups or between-groups. A slightly different experiment might involve people performing different levels of the same experiment. For example, we may be interested in finding out if people recognise real English words more quickly than they do pseudowords (words which follow the same rules of English but have no meaning) or non-words (words which do not follow the rules of English). This is called a lexical decision task. Here, every individual would respond to each type of word (but might be quicker responding to some types of word than others). Because each individual is exposed to the same condition of the experiment (each type of word), the design is called repeated measures or within-groups. There are advantages to using both types of design: independent groups and repeated measures. For statistical reasons, it may be easier to obtain significant results by employing a repeated measures design because this approach eliminates the amount of variability that exists between data from different individuals. Because each participant acts as his or her control (that is, completes each condition in the experiment), there is less variability in the data (such as sex, age and personality differences or the ability to respond quickly to visual stimuli or the tendency to think better in the morning than in the afternoon, etc.). Independent groups designs are advantageous when you do not want to expose the same individuals to the same conditions. For example, if we wanted to compare the effect of fat, carbohydrate and protein intake on people’s ability to react quickly to visual stimuli (because
we hypothesised that certain foods made you drowsy), there would be disadvantages to having them all eat each different type of food (to begin with, if they were tested on different days, they may get better on the reaction time tasks because of practice; secondly, because different food is presented on each occasion, they may become suspicious). An independent groups design would help to eliminate these problems. Such designs are useful to medicine and the study of treatment for mental illness (as you will see in Chapter 18). A mentally ill group would take treatment A, another group treatment B, another group a placebo (we will come on to this later) and a final group would receive no treatment. If treatment A is successful, there should be a difference in outcome between this group and others in the study. Imagine that you were a researcher who was interested in discovering whether people’s cognitive ability declined with age. You take five groups of adults: 20–30-year-olds, 31–40-year-olds, 41–50-year-olds, 51–60-year-olds and the over-61-year-olds. You administer a series of tests which measures a range of cognitive abilities such as verbal and visuospatial ability. You find that whereas most of the over-61 group perform more poorly at most of the tests than do the other groups, they do better at some of the verbal tests such as vocabulary. What do you conclude from this study? If you conclude that verbal ability does not decline as rapidly as other abilities with age, you would be wrong. Can you think why? (The answer appears in Chapter 11.) Using the same example, what would be the theory and what would be the hypothesis in this experiment? What would be the independent and dependent variables? Another approach to studying behaviour might be to conduct an experiment under laboratory or naturalistic conditions. In a laboratory experiment, the experimenter has control over most of the variables that they think will affect the outcome of the experiment. For example, we could design an experiment in which the effect of ambient noise on work performance was measured. We could expose individuals to specific noises at specific levels at specific times while they completed specific tasks and questionnaires assessing mood. Alternatively, we could set up a field experiment in which participants would be observed under fairly ‘natural’ conditions. For example, we might compare the effects of different office lighting conditions, or the weather, on individuals’ mood and productivity. The important feature of naturalistic observations is that the observer remains in the background and does not interfere with the people (or animals) being observed. In some cases, psychologists do interfere with a situation in a natural setting. For example, Chapters 15 and 16 describe some experiments designed to discover what factors determine whether bystanders come to the aid of people who have been hurt or who are in distress. An ‘accident’ is
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staged, and the behaviour of passers-by is surreptitiously observed. Although studies such as these take place outside the laboratory – at job sites or on the street – they are experiments, not naturalistic observations. Such experiments might be called quasi-field studies.
Variables: what is studied and measured activit
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Variables are things that have a particular value but which can vary. Scientists either measure or yp manipulate the values of variables. Manipulate sych literally means ‘to handle’ (from manus, ‘hand’). Psychologists use the word ‘manipulate’ to refer to setting the value of a variable for experimental purposes. The results of this manipulation determine whether the hypothesis is true or false. Direct manipulation of an independent variable, for example, would involve placing individuals into different treatment groups, such as drug A, drug B, a placebo and no drug. Indirect manipulation would involve differentiating individuals with different personality types. For example, we might be interested in whether individuals low, medium or high in trait anxiety (the degree of anxiety they habitually feel) selectively attend to anxiety-related stimuli (such as pictures of snakes, spiders, blood and so on). Or we might look at the effect of positive mood on risk-taking. We would assemble four groups of volunteers to serve as participants. We manipulate mood by having participants watch a comedy film (which would put participants in a positive mood), an unpleasant film (which would put participants in a negative mood) or a neutral film (which would not be expected to influence participants’ mood negatively or positively). We would have a fourth group which would watch no film (the control group). We would then examine the effect of this measure (mood) on risk-taking, such as the amount spent gambling at roulette (taking care, of course, to ensure that our ‘manipulation’ worked). This experiment examines the effect of one variable on another. Here, the variable that we manipulate (mood) is called the independent variable. We could also have a second independent variable, such as the sex of the gambler (Do men or women gamble more? Would we have a good reason for hypothesising a sex difference?) The variable that we measure (risk-taking) is the dependent variable. An easy way to keep the names of these variables straight is to remember that a hypothesis describes how the value of a dependent variable depends on the value of an independent variable. Our hypothesis proposes that increased gambling depends on the individual’s level of mood. Suppose that you were interested in studying the effects of sleep deprivation on learning ability. Which of these two variables would be the independent ee
variable and which would be the dependent variable? How might you define these variables operationally? You can see the relationship between the two variables illustrated in Figure 2.1. Sometimes, we want to understand the causes of behaviour in more than one specific situation. Thus, the variables that hypotheses deal with are expressed in general terms. Independent and dependent variables are categories into which various behaviours are classified. For example, we would probably label all of the following behaviours as ‘interpersonal aggression’: hitting, kicking, throwing something at someone. Presumably, these behaviours would have similar causes. A psychologist must know enough about a particular type of behaviour to be able to classify it correctly. Although one of the first steps in psychological investigation involves naming and classifying behaviours, we must be careful to avoid committing the nominal fallacy or reification. The nominal fallacy refers to the erroneous belief that one has explained an event simply by naming it (nomen means ‘name’). Classifying a behaviour does not explain it; classifying only prepares us to examine and discover events that cause a behaviour. For example, suppose that we see a man frown and shout at other people without provocation, criticise their work when really it is acceptable, and generally act unpleasantly towards everyone around him. Someone says, ‘He’s really angry today.’ Does this statement explain his behaviour? It does not; it only describes the behaviour. To say that he is angry suggests that an internal state is responsible for his behaviour – that anger is causing his behaviour. But all we have observed is his behaviour, not his internal state. Even if he is experiencing feelings of anger, these feelings still do not explain his behaviour. What we really need to know is what events made him act the way he did. Perhaps he has a painful toothache. Perhaps he had just learned that he was passed over for a promotion. Perhaps he had a terrible fight with his wife. Perhaps he had just read a book that advised him to be more assertive. Events like these are causes of both the behaviour and the feelings. Unless they are discovered, we cannot say that we have explained his behaviour. The
INDEPENDENT VARIABLE (manipulated by the experimenter)
DEPENDENT VARIABLE (measured by the experimenter)
POSITIVE MOOD
INCREASED RISK-TAKING
Figure 2.1 Independent and dependent variables described in the mood and risk-taking experiment.
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task of a psychologist is to determine which of the many events that occurred before a particular behaviour caused that behaviour to happen.
Operational definitions This translation of generalities into specific operations is called an operational definition: independent variables and dependent variables are defined in terms of the operations an experimenter performs to set their values or to measure them. In our proposed experiment, for example, the operational definition of the independent and dependent variables might be:
• Independent variable: participants’ mood was induced by watching pleasant, neutral or unpleasant video films; a control group watched none of the films. • Dependent variable: participants’ risk-taking behaviour was measured by monitoring the amount of money spent betting on the outcome of a roulette wheel when the probability of winning was high and when it was low. Providing an operational definition of variables is a hallmark of well-conducted research. If research is to be understood, evaluated and replicated by other people (step 5 of the scientific method described at the beginning of this chapter), the investigator must provide others with a thorough and adequate description of the procedures used to manipulate the independent variable and to measure the dependent variable. For example, a complete definition of the dependent variable (risk-taking) would have to include a detailed description of the type of gambling task and the probability of winning. There are many ways to translate a general concept into a set of operations. We might decide to adopt a different measure of mood, such as having participants
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complete a mental arithmetic task and inform them that they did well or badly (regardless of how they actually performed). This might also be expected to increase or decrease mood. We might choose a different measure of risk-taking such as asking participants to make decisions about a hypothetical risky treatment for a disease that they have (hypothetically) developed. Which operational definition of mood and risk-taking do you think is correct? Is there only one correct definition in this case? What these questions address is the issue of validity.
Validity The validity of an operational definition refers to how appropriate it is – how accurately it represents the variable whose value has been manipulated or measured. You’ll sometimes find the term ‘ecological validity’ being used: this refers to the degree to which the experimental context accurately presents that which the experimenter wants to reproduce. If you set up an experiment to monitor how much people laughed at a comedy, for example, and also measured their brain electrical activity and heart rate, which means attaching wires with electrodes to the head, fingers and chest, would this accurately represent the context in which a person would normally laugh at a comedy programme? The experience could be reasonably said to lack ecological validity. Given enough time, the validity of an operational definition will emerge (or so we hope). If different investigators define the variable in slightly different ways but their experiments yield similar results, we become more confident that the research is leading to an understanding of the phenomena we are studying. The issue of validity is illustrated, famously, by the Barnum effect. The Psychology in Action box tells you more.
Psychology in action – The Barnum effect compensate for them. You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations.
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You are the type of person who has a tendency to be critical of yourself. You have a great need for other people to like and admire you but you pride yourself on being an independent thinker and do not accept others’ statements without satisfactory proof. You have a great deal of unused capacity which you have not turned to your advantage. While you have some personality weaknesses, you are generally able to
Does this description accurately reflect your own personality? It probably does. More than that, it probably applies to the majority of the population. These are universally valid statements which refer to nothing specific but to general feelings and beliefs that could apply to almost everyone. That most people believe that these vague personality descriptions accurately reflect their own personality is called the Barnum effect (Meehl, 1956). The phenomenon is named after Phineas T. Barnum, the great American circus showman, who declared
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Research has shown that highly intelligent readers who are attracted to the boxed off sections of introductory psychology tivit c textbooks, have certain personalities. This personality a ee evaluation is presented below – see how much or how yp sych little you disagree with it. h syc la
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Psychology in action – Continued
The circus showman, P.T. Barnum, who gave his name to the Barnum effect. Source: Popperfoto/Getty Images.
that there was a ‘sucker born every minute’ and believed that his entertainments provided ‘a little something for everybody’. The Barnum effect is seen clearly when individuals accept that ‘generalized, vague, bogus descriptions of themselves which have high base-rate occurrence in the general population’ are correct (Furnham and Schofield, 1987). The phenomenon has a long history in psychology and a less honourable one among proponents of pseudoscience and pseudotherapy. Any clairvoyant or fortune-teller will make cunning use of the Barnum effect to dupe credulous punters. This is not surprising: people have been found to be more accepting of generalised feedback than actual, factual feedback (Merrens and Richards, 1970). A study of 68 personnel managers in the 1950s highlights the way in which we can accept the most vague statements about our personality as reflecting reality. Stagner (1958) administered personality tests to these managers and gave them 13 bogus statements that were assumed to represent actual feedback about their personality from the tests. The statements are listed in Table 2.1. See how many you agree with.
Table 2.1 The Barnum effect 1: personnel managers’ reactions to their ‘personality analysis Judgements as to accuracy of item (% choosing) Amazingly accurate You have a great need for other people to like and admire you You have a tendency to be critical of yourself You have a great deal of unused capacity wihch you have not turned to your advantage While you have some personality weaknesses, you are generally able to compensate for them Your sexual adjustment has presented problems for you Disciplined and self-controled outside, you tend to be worrisome and insecure inside At times you have serious doubts as to whether you have made the right decision or done the right thing You prefer a certain amount of change and variety and become dissatisfied when hemmed in by restrictions and limitations You pride yourself as an independent thinker and do not accept others statements without satisfactory proof You have found it unwise to be too frank in revealing yourself to others At times you are extroverted, affable, sociable, while at other times you are introverted, wary and reserved Some of your aspriations tend to be pretty unrealistic Security is one of your major goals in life
Rather About half good and half
More wrong Almost entirely than right wrong
39 46
46 36
13 15
1 3
1 0
37
36
18
1
4
34 15
55 16
9 16
0 33
0 19
40
21
22
10
4
27
31
19
18
4
63
28
7
1
1
49
31
12
4
4
31
37
22
6
4
43 12 40
25 16 31
18 22 15
9 43 9
5 7 5
Source: Furnham, A., The Barnum effect I: Personnel managers’ reactions to their ‘personality analysis’. Complementary Therapies in Medicine, 1994, 2, 1–4. Copyright 1994, reprinted with permission from Elsevier.
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Psychology in action – Continued When asked to rate how strongly the participants agreed with these statements, almost all indicated that they believed them to some extent and one-third regarded their profile as a ‘good’ reflection of their character. For some statements such as, ‘You prefer a certain amount of change and variety . . .’, and ‘While you have some personality weaknesses . . .’, over 80 per cent of participants expressed agreement with them. In an ingenious spin on the Barnum phenomenon, Furnham (1994) set up an experiment in which undergraduates gave samples of their hair to an experimenter. A week later the participants were given a ‘trichological analysis’ – 24 bland statements regarding their health based on the hair sample – that was totally bogus. Most students thought that these randomly applied statements were very accurate.
Control of independent variables If a scientist performs an experiment and finds that manipulating the value of the independent variable changes the dependent variable, the scientist can conclude that there is a cause-and-effect relation between the variables. That is, changes in the value of the independent variable cause changes in the value of the dependent variable. In designing an experiment, the experimenter must manipulate the value of the independent variable and only the independent variable. For example, if we want to determine whether noise has an effect on people’s reading speed, we must choose our source of noise carefully. If we use the sound from a television set to supply the noise and find that it slows people’s reading speed, we cannot conclude that the effect was caused purely by noise. We might have selected an interesting programme, thus distracting the participants’ attention from the material they were reading. If we want to do this experiment properly, we should use noise that is neutral and not a source of interest by itself, for example, noise like the ‘sssh’ sound that is heard when an FM radio is tuned between stations. In this example, we intended to test the effects of an independent variable (noise) on a dependent variable (reading speed). By using a television to provide the noise, we were inadvertently testing the effects of other variables besides noise on reading speed. We introduced unwanted variables in addition to the independent variable. Schwartz (1999) cites a study showing that when respondents were asked to determine the causes of mass murder reported in newspapers, those doing so on notepaper headed ‘Institute of Personality’ cited more reasons related to personality whereas those doing so on notepaper headed ‘Institute of Social Science’ gave more
What does research on the Barnum effect tell us? First, it shows us that most individuals are inclined to accept bland feedback about themselves. Secondly, it shows us that the validity of a test involves more than intuitively ‘knowing’ that a test measures something. Most individuals – unless they knew about the Barnum effect – would have regarded the statements at the beginning of this section as true and might have accepted the statement that intelligent but sceptical readers are drawn to boxed-off areas of textbooks. This statement is, of course, nonsense. Thirdly, and perhaps most importantly, the Barnum effect shows us that we should always adopt a sceptical and questioning approach to statements made about human behaviour – even to this last statement.
context-social related reasons for the crime. This example, and others in the review, shows that even small details in the conduct of research can influence respondents’ answers and thus affect validity.
Confounding and counterbalancing One of the meanings of the word ‘confound’ is to fail to distinguish. If an experimenter inadvertently introduces one or more unwanted independent variables, they cannot distinguish the effects of any one of them on the dependent variable. That is, the effects of the variables will be confounded and this is called the confounding of variables. It is often difficult to be sure that independent variables are not confounded. We must be certain that when we manipulate the independent variable that variable only, and no other variable, is affected. One method of addressing confounding variables is called counterbalancing, which means to ‘weigh evenly’. Imagine that an experimenter decided to investigate the effect of a memory-enhancing drug on people’s ability to remember concrete and abstract nouns. An experiment is designed in which three groups of people – one taking the drug, another taking a harmless pill and a control group which takes nothing – complete a word recognition experiment. For all groups, the concrete words are presented in the first part of the experiment and the abstract words are presented in the second half. To the experimenter’s surprise, although the drug group’s performance is better than the others’, all groups have more difficulty in remembering the abstract nouns. Does this finding mean that individuals find abstract nouns less memorable? The answer is that, on the basis of the design of the experiment, we cannot know. Because the abstract words
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always appeared in the second half of the experiment, it is possible that the groups simply felt more tired towards the end of the experiment and that their fatigue influenced their recognition scores; they may even have become more bored towards the end of the experiment. Perhaps, having been used to memorising concrete nouns, the shift to a different type of word interfered with the individuals’ memory strategy. A solution would be to counterbalance the presentation of the types of word so that some individuals received the abstract nouns first followed by the concrete nouns whereas others received the concrete nouns first. If the original results were attributable to tiredness or fatigue then the same decrease in recall should be seen in the second half of the experiment. If individuals continue to recall abstract nouns less frequently than concrete nouns, then the result is not due to the effects of the confounding variables of tiredness and fatigue. Having carefully designed a study, we must then decide how best to conduct it. This brings us to step 3 of the scientific method: performing the experiment. We must decide what participants will be used, what instructions will be given, and what equipment and materials will be used. We must ensure that the data collected will be accurate.
Reliability If the procedure described by an operational definition gives consistent results under consistent conditions, the procedure is said to have high reliability. For example, measurements of people’s height and weight are extremely reliable. Measurements of their academic aptitude (by means of standard, commercial tests) are also reliable, but less so. Achieving reliability is usually much easier than achieving validity. Reliability is mostly a result of care and diligence on the part of researchers in the planning and execution of their studies. Alert, careful experimenters can control most of the extraneous factors that might affect the reliability of their measurements. Conditions throughout the experiment should always be as consistent as possible. For example, the same instructions should be given to each person who participates in the experiment, all mechanical devices should be in good repair, and all assistants hired by the experimenter should be well trained in performing their tasks. Noise and other sources of distraction should be kept to a minimum. Another issue that affects reliability is the degree of subjectivity involved in making a measurement. In the experiment described above – the investigation of the effects of mood on creativity – our definition of mood was objective; even a non-expert could follow our procedure and obtain the same results. But researchers often attempt to study variables whose measurement is subjective, that is, it requires practical judgement and expertise.
For example, suppose that a psychologist wants to count the number of friendly interactions that a child makes with other children in a group. This measurement requires someone to watch the child and count the number of times a friendly interaction occurs. But it is difficult to be absolutely specific about what constitutes a friendly interaction and what does not. What if the child looks at another child and their gazes meet? One observer may say that the look conveyed interest in what the other child was doing and so should be scored as a friendly interaction. Another observer may disagree. The solution in this case is, first, to try to specify as precisely as possible the criteria to be used for defining an interaction as friendly in order to make the measurement as objective as possible. Then, two or more people should watch the child’s behaviour and score it independently, that is, neither person should be aware of the other person’s ratings. If their ratings agree, we can say that the scoring system has high interrater reliability. If they disagree, interrater reliability is low, and there is no point in continuing the study. Instead, the rating system should be refined and the raters should be trained to apply it consistently. Any investigator who performs a study that requires some degree of skill and judgement in measuring the dependent variables must do what is necessary to produce high interrater reliability. There are other ways in which a researcher can test the reliability of their data. For example, say that we wanted to examine whether an individual’s responses on a personality questionnaire were reliable. One method of determining this might be to divide the questionnaire and compare the responses of the participant in each of the two sections of the questionnaire. If there is strong agreement between scores from each half, the questionnaire results are said to be reliable. This is called split-half reliability because the measure (the personality questionnaire) is split and responses to the two split parts compared. But what if the questionnaire is too short for split-half reliability to be tested or the test measures many different factors (as an intelligence test does)? One way of testing reliability in such circumstances might be to administer the test at one session and then again at another session, some time apart. If the test is reliable, it should yield the same scores at the first as at the second session. This is called test–retest reliability. However, can you see a possible confound here? Imagine if you were to examine the test–retest reliability of an IQ test. The scores at the second session may be better because the participant has already undertaken the same test once. So, the test may be reliable but the data obtained from the test suggest that it is not. Can you think of a way of circumventing this problem? (Chapter 11, Intelligence and thinking, takes up this issue in more detail.)
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Selecting participants So far, we have dealt with what we, as researchers, would do – what hypothesis we would test, how we would design the experiment, and how we would obtain valid and reliable measurements. Now let us turn to the people who will participate in our experiment: our participants. How do we choose them? How do we assign them to the experimental or control group? These decisions must be carefully considered because, just as independent variables can be confounded, so can variables that are inherent in participants whose behaviour is being observed. Consider the following example. A lecturer wants to determine which of two teaching methods works best. She teaches two courses in introductory psychology, one that meets at 9.30 a.m. and another that meets at 4 p.m. She uses one teaching method for the morning class and another for the afternoon class. At the end of the term she finds that the final examination scores were higher for her morning class. She concludes that from now on she will use that particular teaching method for all of her classes. However, there is a problem. Think about what this might be before you read the next sentence. The two groups of participants for the experiment are not equivalent. People who sign up for a class that meets at 9.30 a.m. are likely to differ in some ways from those who sign up for a 4 p.m. class. Some people prefer to get up early whereas others prefer to sleep late. Perhaps the university sports department schedules some kinds of activity late in the afternoon, which means that students interested in participating in these activities will not be able to register for the 4 p.m. class. For many reasons, the students in the two classes will probably not be equivalent. Therefore, we cannot conclude that the differences in their final examination scores were caused solely by the differences in the teaching methods.
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Of course, in the past ten years or so, researchers have also been exploiting the internet as a source of participants. It can be a quick and very effective way of recruiting large numbers of participants. It has advantages over paper-and-pencil (PP) versions of tests – the error rate is lower (electronic responses are more legible than written ones) and the response/take-up rate is higher. However, there is evidence that internet participants leave out more items on test inventories and choose the extreme ends of responding, selecting strongly agree/disagree more often than do PP participants. All psychological experiments use samples – human or animal – and researchers usually know the type of sample they need. If they are testing the efficacy of a drug or the effectiveness of a type of rehabilitation following brain injury, for example, they include samples with specific characteristics. Most psychological researchers, however, recruit opportunity samples: people willing to give up their time and participate in research. But how representative are these opportunity samples? The Controversies in Psychological Science section takes up this topic. Participants must be carefully assigned to the various groups used in an experiment. The usual way to assign them is by random assignment. One way to accomplish random assignment is to list the names of the available participants and then to toss a coin for each one to determine the participant’s assignment to one of two groups. More typically, the assignment is made by computer or by consulting a list of random numbers. We can expect people to have different abilities, personality traits and other characteristics that may affect the outcome of the experiment, but if people are randomly assigned to the experimental conditions, these differences should – according to the principle of random sampling – be equally distributed across the groups.
Controversies in Psychological Science – How representative are samples in psychological research? As a psychology student, you will inevitably be asked to participate in a psychology experiment. This may be part of your research methods or other course; or it may be an experiment run by your tutor or department. In fact, if you look at the method sections of scientific articles published in psychology, you will find that the majority of these reports recruit participants just like you: psychology students. This is a source of concern for some psychologists because the findings from such a group may not be representative of the behaviour of
other sections of the population. How representative, therefore, are examples in psychological research?
The evidence In a study of recruits from undergraduate psychology classes who participate in psychology experiments, Quinones-Vidal et al. (2004) found that of all papers in the prestigious Journal of Personality and Social Psychology (a leader in its field) 92 per cent originated in the US and Canada and 99 per cent from Western countries.
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Controversies in Psychological Science – Continued Another study, which investigated the degree of over-representation of psychology students in psychology research published in the British Journal of Social Psychology (BJSP) and the British Journal of Psychology (BJP) in 1995 and 1996, found that of 107 studies 29 per cent used non-student adults and 15.9 per cent of the experiments were in a real-life environment (Banyard and Hunt, 2000). Twenty-eight per cent were based in a laboratory and 26.2 per cent were conducted in other parts of a university such as a lecture hall. Pressure to participate was evident in 58 per cent of the studies (students would take part to obtain course credit or because experiments were a course requirement). Volunteers were used in 17.8 per cent of the studies. Over 70 per cent of papers in BJSP used self-report measures whereas over 50 per cent of BJP studies used laboratory-based measures. One-third of studies did not record how the sample was recruited and only 33 per cent of the 18,635 people who participated in the experiments were coded for their sex. Ethnicity was considered in only one study. The study highlights some important points to remember when reading and explaining the findings of research (although this analysis was based on two journals published in two
years). The authors state that using students for research is acceptable but they query how representative this sample is. The view is echoed in another study of ethnic representation among samples in applied psychology studies (Case and Smith, 2000). Case and Smith found that in 2,536 articles from 14 applied psychology journals taken in a 5-year period, almost 40 per cent indicated the ethnicity of the participant. In the articles that did include details of ethnicity, there was an over-representation of African Americans and an under-representation of Hispanic Americans (compared with the actual number of Hispanic people in the population).
Conclusion ‘Because psychological research must be relevant and appropriate for individuals from diverse ethnic backgrounds,’ the authors argue, ‘researchers must use samples that adequately represent diverse populations.’ They go on to argue that if we are to find out what works for whom, then we must include factors such as ethnicity in studies of psychological processes. When you read primary sources in psychology – journal articles – take some time to study the sample used and think of why the authors chose this sample.
Response bias... – An international perspective Response bias – responding to a questionnaire in a way that is not genuine or honest but in an irrelevant way such as always responding ‘yes’ to a series of questions – is an important concept in research methods because it can skew results and tell researchers something which is not very meaningful. A Dutch study of six European countries has found that response bias varies by cultures. Researchers used existing data from a multinational marketing survey to examine response bias in participants from Greece, Italy, Spain, France, Germany and the UK (Van Herk et al., 2005). They found that unlike participants from north-western European countries, those from
Researchers must remain alert to the problem of confounding subject variables even after they have designed an experiment and randomly assigned participants to the groups. Some problems will not emerge until the investigation is actually performed. Suppose that an experimenter was interested in learning whether anger decreases a person’s ability to concentrate. The experi-
Mediterranean countries showed an abnormally high tendency to agree than disagree with answers (acquiescence), and a greater likelihood to chose extreme response categories (e.g. selecting 1 or 5 on a 5-point scale). Greek participants, in particular, significantly exhibited these response biases. Spain and Italy scored higher on these two biases than did the UK, France and Germany. The British were the least acquiescent. The authors suggest that such differences might reflect the different types of cultures in these countries: collectivistic versus individualistic. The more individualistic the societies were, the less acquiescent they seemed.
menter acts rudely towards the participants in the experimental group, which presumably makes them angry, but treats the participants in the control group politely. After the rude or polite treatment, the participants watch a video screen that shows a constantly changing display of patterns of letters. Participants are instructed to press a button whenever a particular letter appears. This vigi-
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lance test is designed to reveal how carefully participants are paying attention to the letters. The design of this experiment is sound. Assuming that the participants in the experimental group are really angry and that our test is a valid measure of concentration, we should be able to make conclusions about the effects of anger on concentration. However, the experiment, as performed under real conditions, may not work out the way it was designed. Suppose that some of our ‘angry’ participants simply walk away. All experimenters are required to tell participants that they are free to leave at any time (and the section on ethics later in this chapter will tell you why); some angry participants might well do so. If they do, we will now be comparing the behaviour of two groups of participants of somewhat different character – a group of people who are willing to submit to the experimenter’s rude behaviour and a group of randomly selected people, some of whom would have left had they been subjected to the rude treatment. Now the experimental group and control group are no longer equivalent. Figure 2.2 illustrates this. The moral of this example is that an experimenter must continue to attend to the possibility of confounded variables even after the experiment is under way. The solution in this case? There probably is none. Because we cannot force participants to continue to participate, there is a strong possibility that some of them will leave. There is also the flip side to this problem, where participants will respond in an unnaturally positive way because this is what they believe the experimenter wants. For example, they may give answers on personality or other questionnaires that portrays them in the best light. This is called social desirability. As you will see in Chapters 15 and 16 (on social psychology), the relationship between
Some subjects leave Experimental group
Treated rudely by experimenter Remaining subjects perform vigilance task Groups are not equivalent
Control group
Treated politely by experimenter
All subjects perform vigilance task
Figure 2.2 A possible problem with the anger and concentration experiment: loss of subjects from the experimental group.
experimenter and participant is sometimes a complex one. Some psychological variables are, by their nature, difficult to investigate.
Participants’ expectations Participants in a psychology experiment are not simply passive participants whose behaviour is controlled solely by the independent variables manipulated by the experimenter. Participants know that they are being observed, and this knowledge is certain to affect their behaviour. This is sometimes known as the Hawthorne effect: the notion that the act of observation can change what it is you are observing. It derives from, ostensibly, a phenomenon that occurred in the Hawthorne Works of the Western Electric Company in Chicago in the 1902s and 1930s. The managers hypothesised that increasing the lighting conditions would increase productivity, which it did but this effect was short-lived. Productivity increases were seen when the lighting conditions changed, as if the workers were aware of the manipulation and worked harder (Adair, 1984). While the Hawthorne effect is not that well established (the name was given to the effect in a book published in 1953 and the original studies were never published; Chiesa and Hobbs, 2008), participants will behave as if an hypothesis is true if they find out the hypothesis. For example, Young et al. (2007) found that if people were given questionnaires on motion sickness to complete before they were exposed to virtual reality displays (which they were told might induce motion sickness), they reported more motion sickness than those who did not complete such questionnaires. Because the study is being run by a psychologist, some participants are unlikely to take what they say at face value and will look for motives hidden behind an apparently simple task. Actually, most experiments are not deceptive at all; they are what they appear to be and ‘deceptive’ studies do not always succeed in fooling the participants. For example, suppose you are a participant in an experiment that was represented as being a learning study. On the table in front of you is an assortment of knives and pistols. The experimenter says, ‘Oh, ignore them. Someone else left them here. They have nothing to do with this study.’ Do you believe her? Probably not, and you will undoubtedly try to figure out how the presence of these weapons is supposed to affect your behaviour. You may suspect that the psychologist is trying to determine whether the presence of weapons will increase your hostility. With this suspicion in mind, you may (1) act naturally, so that you will not spoil the experiment; (2) act aggressively, to help the experimenter get the results you think she wants; or (3) act non-aggressively, to prove that you are immune to the effects of
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objects associated with violence. The results of this study may not show the effects of the presence of weapons on aggression but, rather, show the relative numbers of people who select strategy 1, 2 or 3 in response to the knowledge that they are being observed. Experimenters must always remember that their participants do not merely react to the independent variable in a simple-minded way. As Chapters 15 and 16 show, these considerations are especially important in social psychology experiments. In some of these studies, the experimenter or the experimenter’s assistants act out roles designed to provide a particular kind of social situation to which the participants are exposed. Obviously, the participants’ interpretation of these situations affects their behaviour.
Single-blind experiments A special problem is posed by experiments in which participants’ behaviour might be affected by their knowledge of the independent variable. Two methods of circumventing this problem are single- and double-blind experiments. For example, suppose that we want to study the effects of a stimulant drug, such as amphetamine, on a person’s ability to perform a task that requires fine manual dexterity. We will administer the drug to one group of participants and leave another group untreated. We will count how many times each participant can thread a needle in a 10-minute period (our operational definition of fine manual dexterity). We will then see whether taking the drug had any effect on the number of needle threadings. But there is a problem in our design. For us to conclude that a cause-and-effect relation exists, the treatment of the two groups must be identical except for the single variable that is being manipulated. In this case the mere administration of a drug may have effects on behaviour, independent of its pharmacological effects. The behaviour of participants who know that they have just taken amphetamine is very likely to be affected by this knowledge as well as by the drug circulating in their bloodstream. To solve this problem, we should give pills to the members of both groups. People in one group will receive amphetamine, and those in the other group will receive an inert pill – a placebo, from the Latin placere, ‘to please’. A physician sometimes gives a placebo to anxious patients to placate them. Participants will not be told which pill they receive. By using this improved experimental procedure called a single-blind study, we can infer that any observed differences in needle-threading ability of the two groups were produced solely by the pharmacological effects of amphetamine. The placebo effect is a strong one – brain imaging studies have found that when people are given a placebo ‘treatment’ for pain, there is a reduction in the activation of brain areas involved in pain (Wager et al., 2004).
Double-blind experiments In a single-blind experiment, only the participants are kept ignorant of their assignment to a particular experimental group; the experimenter knows which treatment each participant receives. Now let us look at an example in which it is important to keep both the experimenter and the participants in the dark. Suppose we believe that if patients with mental disorders take a particular drug, they will be more willing to engage in conversation. The drug is given to some patients and a placebo is administered to others. We talk with all the patients afterwards and rate the quality of the conversation. But ‘quality of conversation’ is a difficult dependent variable to measure, and the rating is therefore likely to be subjective. The fact that the experimenters know which patients received the drug means that we may tend to give higher ratings to the quality of conversation with those patients. Of course, we would not intentionally cheat, but even honest people tend to perceive results in a way that favours their own preconceptions. The solution to this problem is simple. Just as the patients should not know whether they are receiving a drug or a placebo, neither should the experimenter. That is, we should carry out a double-blind study. Someone else should administer the pill, or the experimenter should be given a set of identical-looking pills in coded containers so that both experimenter and patient are unaware of the nature of the contents. Now the ratings cannot be affected by any preconceived ideas the experimenter may have. The double-blind procedure does not apply only to experiments that use drugs as the independent variable. Suppose that the experiment just described attempted to evaluate the effects of a particular kind of psychotherapy, not a drug, on the willingness of a patient to talk. If the same person does both the psychotherapy and the rating, that person might tend to see the results in a light that is most favourable to their own expectations. In this case, then, one person should perform the psychotherapy and another person should evaluate the quality of conversation with the patients. The evaluator will not know whether a particular patient has just received psychotherapy or is a member of the control (untreated) group. The expectations of experimenters can influence results in studies with laboratory animals as much as in studies with human participants. Rosenthal and Fode (1963) demonstrated the influence of expectations by having students train rats to learn the way through a maze. They told half the students that they had ‘stupid’ rats and the other half that they had ‘smart’ rats. In fact, there were no differences in the animals’ abilities. However, an analysis of the results indicated that the ‘smart’ animals learned faster than the ‘stupid’ ones. The students’ expectations clearly affected their rats’ performances.
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Presumably, the students who had ‘smart’ rats took better care of them, which affected the animals’ performances.
Correlational studies To be certain that a cause-and-effect relation exists, we must perform an experiment in which we manipulate the independent variable and measure its effects on the dependent variable. But there are some variables, especially participant variables, that a psychologist cannot manipulate. For example, a person’s sex, genetic history, income, social class, family environment and personality are obviously not under the psychologist’s control. Nevertheless, these variables are important and interesting because they often affect people’s behaviour. Because they cannot be manipulated, they cannot be investigated in an experiment. A different method must, therefore, be used to study them: a correlational study. The basic principle of a correlational study is simple: for each member of a group of people we measure two or more variables as they are found to exist, and we determine whether the variables are related by using a statistical procedure called correlation. Correlational studies are often done to investigate the effects of personality variables on behaviour. For example, we may ask whether shyness is related to daydreaming. Our hypothesis is that shy people tend to daydream more than people who are less shy. We decide how to assess a person’s shyness and the amount of daydreaming that they engage in each day, and we then take the measure of these two variables for a group of people. If shy people tend to daydream more (or less) than people who are not shy, we can conclude that the variables are related. Imagine that we do find that shy people spend more time daydreaming. Such a finding tells us that the variables are related – we say they are correlated – but it does not permit us to make any conclusions about cause and effect. Shyness may have caused the daydreaming, or daydreaming may have caused the shyness, or perhaps some other variable that we did not measure caused both shyness and an increase in daydreaming. In other words, correlations do not necessarily indicate cause-and-effect relations. A good illustration of this principle is provided by a correlational study that attempted to determine whether membership in the boy scouts would affect a person’s subsequent participation in community affairs (Chapin, 1938). The investigator compared a group of men who had once been boy scouts with a group of men who had not. He found that the men who had been boy scouts tended to join more community affairs groups later in life. The investigator concluded that the experience of being a boy scout increased a person’s tendency to join community organisations. However, this conclusion is not warranted. Can you see why? All we can say is that
people who join the boy scouts in their youth tend to join community organisations later in life. It could be that people who, for one reason or another, are ‘joiners’ tend to join the boy scouts when they are young and community organisations when they are older. To determine cause and effect, we would have to perform an experiment. For example, we would make some boys join the boy scouts and prevent others from doing so, and then see how many organisations they voluntarily joined later in life. Because we cannot interfere in people’s lives in such a way, we can never be certain that being a boy scout increases a person’s tendency to join community organisations later. The news media often report the results of correlational studies. We are led to believe that because two variables are correlated, one event causes another. But this conclusion may not be true. For example, a news magazine reported a study in which small companies that make heavy use of computers were found to have productivity levels 2.5 times greater than companies that did not. Can we conclude that the heavy use of computers is the cause of the increased productivity? No, we cannot; correlation does not prove causation. Is it likely that the two types of small company (those that make heavy use of computers and those that do not) are identical in all other ways? Probably not. For example, companies that make heavy use of computers can afford to do so, and they can probably afford to make other investments that might increase productivity. In addition, these companies may also have managers who are up to date in other respects, and having modern ideas about other aspects of running a company may also improve productivity. The use of computers may indeed increase productivity, but the information presented does not permit us to come to this conclusion. Can anything be done to reduce some of the uncertainty inherent in correlational studies? The answer is yes. When attempting to study the effects of a variable that cannot be altered (such as sex, age, socio-economic status or personality characteristics) we can use a procedure called matching. Rather than selecting participants randomly, we match the participants in each of the groups on all of the relevant variables except the one being studied. For instance, if we want to study the effects of shyness on daydreaming, we may gather two groups of participants, shy and non-shy. We select the participants in each group in such a way that the effects of other variables are minimised. We make sure that the average age, intelligence, income and personality characteristics (other than shyness) of the two groups are the same. If we find that, for example, the shy group is, on average, younger than the non-shy group, we will replace some of the people in the shy group with older shy people until the average age is the same.
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If, after following this matching procedure, we find that shyness is still related to daydreaming, we can be more confident that the relation is one of cause and effect and that the differences between the two variables are not caused by a third variable. The limitation of the matching procedure is that we may not know all the variables that should be held constant. If, unknown to us, the two groups are not matched on an important variable, then the results will be misleading. In any case, even the matching procedure does not permit us to decide which variable is the cause and which is the effect; we still do not know whether shyness causes daydreaming or daydreaming causes shyness. The strengths and limitations of correlational studies will become evident in subsequent chapters in this book. For example, almost all studies that attempt to discover the environmental factors that influence personality characteristics or the relation between these characteristics and people’s behaviour are correlational.
tain how an individual behaved before the accident; there is no control over the degree and type of injury; and there is the possibility that personal characteristics (such as medication use, sex, age, socio-economic status, IQ) could influence results (Shallice, 1988; Martin, 2006). The single-participant research design (SPRD) does have advantages, however. One is that by continuously studying a participant over an extended period, we can be sure that the sample of behaviour that is measured is representative of the participant’s typical behaviour. This also allows for easy replication although there are some studies which cannot be properly replicated – a learning intervention, for example, cannot be easily unlearned. The SPRD approach allows us to see the natural variability in the participant’s behaviour – marked changes in behaviour that are not attributable to experimental manipulation. SPRDs also involve participants as their own controls, thereby reducing the individual difference that could account for differences between (and within) large groups.
Single-case studies
Generalising from data
Not all investigations in psychology use groups of participants. Single-case study research explores the behaviour of individuals, and for some phenomena this method is very effective. Single-case study research can involve either experiments or correlational studies. Ebbinghaus’s studies of memory, for example, were based on studies of individuals (usually, Ebbinghaus himself). Similarly, much of B.F. Skinner’s work was based on small numbers of participants. In a single-case study, psychologists can take advantage of events that have occurred outside their control and the most common of these are found in the field of neuropsychology. For example, a patient known as HJA was a businessman who had suffered a stroke and had consequently sustained damage to specific regions of his brain. HJA’s behaviour after the damage was perceptually unusual. Although some aspects of his visual perception were preserved, he would have difficulty in recognising objects. For example, he would spend up to six hours making painstaking drawings of objects which he would be unable to name (Humphreys and Riddoch, 1987a, b). This is a disorder called visual agnosia, a specific deficit in the ability to perceive objects, described in more detail in Chapter 6. By conducting single-case studies of patients like HJA, psychologists can explore the behavioural consequences of unusual events or actions that the patient has suffered. Single-case studies have contributed substantially to our knowledge of neuropsychology, the study of the relationship between the activity of the brain and its function, although this method has been criticised. For example, there is frequently no way of knowing for cer-
When we carry out an experiment or a correlational study, we probably assume that our participants are representative of the larger population. In fact, a representative group of participants is usually referred to as a sample of the larger population. If we study the behaviour of a group of 5-year-old children, we want to make conclusions about 5-year-olds in general. We want to be able to generalise our specific results to the population as a whole – to conclude that the results tell us something about human nature in general, not simply about our participants. Many researchers recruit their participants from introductory courses in psychology because this is a convenient way of obtaining participants. The results of studies that use these students as participants can be generalised only to other groups of students who are similarly recruited. In the strictest sense, the results cannot be generalised to students in other courses, to adults in general, or even to all students enrolled in introductory psychology – after all, students who volunteer to serve as participants may be different from those who do not. Even if we used truly random samples of all age groups of adults in our area, we could not generalise the results to people who live in other geographical regions. If our ability to generalise is really so limited, is it worthwhile doing psychological research? In reality we are not so strictly limited. Most psychologists assume that a relation among variables that is observed in one group of humans will also be seen in other groups as long as the sample of participants is not especially unusual. For example, we may expect data
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obtained from prisoners to have less generality than data obtained from college students.
Application of psychological research There is sometimes a distinction made in the sciences between applied and pure aspects of research. Pure research is research carried out for its own ends; the implications or consequences of such research are not known but it is designed simply to find out how something works or behaves (or does not). Applied research, on the other hand, is designed to have a practical application. Often in psychology (as in most other sciences), this dichotomy is false. Pure research can often have surprising practical applications: it depends on how creative the scientist is in finding such applications. Throughout this book, you will find examples of research that seems to fall into these categories. When you do, reflect on what you have read and try to see the point of having conducted that piece of research. The Psychology in Action sections in this book show how dry, academic, laboratory-based research can tell us much about how we behave ‘outside’ the laboratory. Should psychological research always have a practical outcome?
Qualitative analysis The majority of research undertaken in psychology is empirical and quantitative. Another approach relies less on these types of data. Some researchers have argued that traditional quantitative techniques do not allow psychologists to explore the richness of human experience, feeling, thought and social interaction. They suggest that this richness is better measured by paying close attention to the ways in which people use words, express feelings and arguments and by allowing individuals to explore ideas in discussion. Themes and ideas can then be interpreted from transcripts of these discussions. This approach is called qualitative analysis and is concerned with ‘meanings, context and a holistic approach to material’ (Hayes, 1997). It is more popular in European research centres than in North America. The BPS’s Qualitative Methods Section was formed in 2006, for example, but a proposal for a new Division of Qualitative Inquiry was rejected by the American Psychological Association in 2008. This approach is called phenomenological because the experience, reactions and feelings of the individual are considered to be of paramount importance. Originally, qualitative analysis emerged as a new paradigm in the 1970s called ethogenics which sought to provide a better method of investigation in psychology (Harré and Secord, 1972). The new approach placed great emphasis on
people’s use of language, especially the ways in which people accounted for their behaviour, thoughts and feelings: to understand real psychology meant analysing real talk (Foster and Parker, 1995) and this talk is, itself, ‘action’; we use words to convey some action (blame, sorrow, anger, etc.). The approach has been used to study the impact of a child’s serious illness on the family (Hopi et al., 2005), how dietary regimes are viewed in people with type 2 diabetes (Peel et al., 2005), and how doctor and patient interact with each other (McCabe et al., 2002). The emphasis in the qualitative approach is not on quantifying data (in many cases this is actively discouraged) but in exploring the quality of data in depth. Some qualitative analysts have insisted that this form of analysis should not involve any numbers or counting at all (Strauss and Corbin, 1990), although this strict criterion is not often adhered to. Many qualitative analyses draw attention to concepts involving quantity such as frequency of utterances. Another important distinction between qualitative and quantitative analysis is that the former views the researcher as being central to the analysis and the process of data collection: they may participate in or facilitate discussion and will analyse the data obtained from their research. The interpretation of the data is also undertaken by the researcher/interviewer. The data for qualitative analysis usually come from group discussions or interviews and there are various methods for conducting qualitative analysis. Some of these are outlined below.
Structured and semi-structured interviews Using the format of an interview to obtain information in psychology is not unusual. Many neuropsychological tests are administered by experimenters in an interviewtype context. When such tests are administered, the researcher keeps to a strict ‘script’ in order to avoid influencing the performance of the respondent. In a sense, this is something like the format of a structured interview. The structured interview is conducted along predefined and predetermined lines with little scope for deviation from a script. The experimenter decides what they want to explore, with little variation between interviews. Many structured interviews may comprise an interviewer reading questions from a questionnaire and soliciting responses from an interviewee. Sometimes, however, it may be interesting and informative to explore interviewees’ responses more deeply while keeping to some overall plan or structure. Semistructured interviews provide such a possibility. The semi-structured interview allows the establishment of rapport with the interviewee by placing less emphasis on the order of questions, where the interviewer is free to
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develop themes and issues raised by the interviewee and where open-ended questions are used. For example, whereas a structured interview might ask, ‘Do you think that racism is caused by a, b, c or d?’, a semi-structured interview might ask, ‘What do you think are the causes of racism?’ It is suggested that funnelling is a useful approach to semi-structured interviews: the interviewer elicits a general opinion and then probes more specific issues relating to this general view. The semi-structured interview has proved to be useful to some qualitative analysts. Others, however, would argue that even a semi-structured format is too restrictive and that in order to elicit and understand genuine thoughts and feelings, you must allow discussion to occur freely (Hammersley, 2008). Such an approach is taken by discourse analysis.
Discourse analysis Discourse analysis is a method which was developed in the mid-1980s to identify thoughts, feelings and themes from transcripts of data derived from conversations involving two or more individuals. Discourse analysis examines what people do with conversation and writing (Potter and Wetherell, 1995). Discourses themselves are linguistic repertoires (Potter and Wetherell, 1987) which vary according to context. The most detailed analysis of discourses would examine the use of sound and verbal devices in conversation as well as mechanisms of persuasion and argument (Edwards and Potter, 1992). Discourse analysis places importance on the use of language and what people mean when they express themselves verbally (Billig, 1997). Such speech acts could be complicated and would require careful analysis in order to discover what was meant. Discourse analysis does not assume that attitudes are stable; in fact, it assumes that ‘giving views’ is relatively unstable and that a person can give one view to one person and a contrary view to another: context, therefore, is important to the interpretation of attitude. A teenage girl’s attitudes towards social issues might be expressed differently to a parent and to a member of her peer group, for example (Billig, 1997). In Table 2.2, Billig outlines the typical discourse analysis which could be performed on these transcripts. Transcripts should be read and reread; the analyst should begin to develop ‘hunches’ or intuitive understanding and they should, after rereading, create index categories of themes and major issues and of conversational details such as interruption or non-verbal agreement.
Conversation analysis As the name suggests, conversation analysis involves the analysis of the content and use of conversation. The
Table 2.2 Suggested procedure for qualitative analysis • Read background material about discursive psychology and topic of interest • Decide on type of data to be studied • Collect data • Collect, listen to and transcribe tape-recordings • Check the transcriptions against the tapes • Read transcriptions • Look for interesting features and develop ‘intuitive hunches’ • Begin indexing themes and discursive features • Write preliminary analysis, testing ‘hunches’ against data • Draft and redraft analyses, making note of counter examples Source: Adapted from M. Billig, Rhetorical and discursive analysis. In N. Hayes (ed.) Doing Qualitative Analysis in Psychology. Hove: Psychology Press, 1997. © 1997. Reprinted by permission of Psychology Press Limited, Hove, UK.
assumption behind conversational analysis (CA) is that talk is action and that it is structurally organised. The focus is less on the content of the talk but on what people do with it – complaining, complementing, news-telling, turn-taking, and so on (Wilkinson and Kitzinger, 2008). Data are collected in ‘naturalistic’ environments – the researcher is not present and the participant is audio- or video-recorded. These data take the form of transcripts, complete with inbreaths, sound stretches, pauses and other example of oral punctuation. An example of how CA has been used to analyse how people use talk is seen in Table 2.3. This is a transcript of an exchange between two friends, Belle and Fanny, one of whom (Belle) has some bad news to break. Take a look at this exchange before reading on. Did you notice something unusual in the conversation? Although it was Belle who had bad news to break, it was Fanny who ‘announced’ the news. CA has revealed that we often do this – the recipient of bad news tends to be the one who raises the matter of bad news, whether it is a cancelled trip or a medical diagnosis (Drew, 1984; Maynard, 1992). In another example of the use of CA, Clayman and Heritage (2002) analysed 4,000 questions asked by journalists in US Presidential Conferences from 1950 to 2000, and found that the questions became less deferential and more combative over time.
Grounded theory Grounded theory was one of the earliest attempts at qualitative analysis and involves establishing a set of strategies for the analysis of data and the construction of theory (Glaser and Strauss, 1967; Charmaz and Henwood, 2008). Individual cases, incidents or experiences are analysed and theories are derived from such analysis (Charmaz, 1990). Unlike discourse analysis, grounded theory actively attempts to develop theory from information obtained
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Table 2.3 The format in which conversation is transcribed in conversation analysis. The first extract shows you a conversation between two friends, one of whom had bad news to break. The second is an exchange between a doctor and a patient which, again, involves the breaking of unwelcome news. Extract 1 (DA: 2 : 10. from Schegloff (1988: 443) The audio file for this data extract can be accessed at:
} 01 Bel: ... I, I-I had something 02 (.) terrible t’tell you.= 03 =So {uh: } 04 Fan: {How t}errible {is it.} 05 Bel: {.hhhhh} 06 (.) 07 Bel: Uh: en worse it could be:. 08 (0.7) 09 Fan: W’y’mean 1da? 10 (.) 11 missing line from photocopy 12 Fan: Wud she do die:?= 13 Bel: = Mm:hm. Extract 2 (8.013), from Maynard (1992: 337–8) 01 Dr: What do you see? as- as his 02 (0.5) difficulty. 03 (1.2) 04 Mo: Mainly his uhm: (1.2) the 05 fact that he doesn’t 06 understand everything. 07 (0.6) and also the fact 08 that his speech (0.7) is 09 very hard to understand 10 what he’s saying (0.3) 11 lot{s of ti}me 12 Dr: { right } 13 (0.2) 14 Dr: Do you have any ideas wh:y it 15 is: are you: d}o yo}u?h 16 Mo: { No } 17 (2.1) 18 Dr: .h okay I (0.2) you know I 19 think we basically (.) in 20 some ways agree with you: 21 (0.6) .hh insofar as we think 22 that (0.3) Dan’s main problem 23 (0.4) .h you know does: 24 involves you know language. 26 Mo: Mm hmm 27 (0.3) 28 Dr: you know both (0.2) you know 29 his- (0.4) being able to 30 understand you know what is 31 said to him (0.4) .h and 32 also certainly also to be 33 able to express:: (1.3) you 34 know his uh his thoughts 35 (1.1) 36 Dr: .hh uh:m (0.6) .hhh in 37 general his development... Source: Wilkinson, S. and Kitzinger, C. (2008) Conversation analysis. In C. Willig and W. Stainton-Rogers (eds) The Sage Handbook of Qualitative Research in Psychology. London: Sage.
from transcripts of conversations. Theorising is made possible by painstaking line-by-line coding of transcripts, by memo-taking and by constructing categories (themes/patterns) from responses. The theory is therefore grounded in what the respondents have had to say. An example of the approach would be the exploration of the loss of self/the expression of self in patients who have suffered traumatic brain injury (Nochi, 1998).
Q methodology One of the more complex of the qualitative techniques, Q methodology is also one of the most numerical and was first developed in the 1930s. It has been described as the systematic study of subjectivity and used to ‘explore the subjective dimension of any issue towards which different points of view can be expressed’ (Stenner et al., 2008, p. 215). In this approach, data are collected in the form of Q-sorts: a collection of statements with which a participant agrees, disagrees or has no opinion about. A researcher might start with a clear question, such as ‘What is your understanding of qualitative research?’ and a number of items that represent this issue are devised (say around 100) and are given to students, qualitative practitioners and so on who sort them according to level of dis/agreement. A reduced number of around 60 will then be given to participants and each is rated on a 13point scale for dis/agreement. The unique feature of Q methodology is that the person becomes the variable. Q methodology has been used in a number of contexts. One study found that the greater the disagreement about the causes of irritable bowel syndrome between the doctors and patients, the greater the patient’s antagonism; the greater the agreement, the more positive the relationship (Stenner et al., 2000).
Limitations of qualitative analysis Qualitative analysis, although not widely used, has become a popular research tool in many areas of psychology where analysis can be used to explore issues such as attitudes to death, racism, the monarchy, sexual identity, chronic illness, work relationships and so on. Currently, qualitative analysis has had little impact outside these areas because of several perceived shortcomings. The most obvious, and difficult to reject, is that the process of qualitative analysis is subjective: the selection, analysis and interpretation of the material is made by the analyst. This introduces an element of bias into the study which could cloud an ‘objective’ analysis of the data. This argument is difficult to challenge effectively, although Hayes (1997) has suggested a ‘halfway house’ solution whereby a theory determined prior to the study may be used to guide later analysis. In this way,
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the study has a pre-stated focus and direction but it also allows for unpredicted insights. Hammersley (1992) has identified several examples of the perceived differences between qualitative and quantitative analysis. For example, it is assumed that the types of data analysed by the two methods are totally different; the environments in which studies take place are different; one focuses on meaning (qualitative), the other on behaviour; quantitative methods adopt natural science as a model whereas qualitative analysis rejects it; one is inductive, the other deductive; one seeks patterns, the other seeks laws and so on. Hayes (1997) has given an excellent account of how this dichotomy may be more imagined than real. For example, she argues that qualitative researchers do sometimes use measures of quantity and that quantitative methods are often applied in naturalistic settings. Qualitative analysts do use conversational analysis to study behaviour as well as meaning. Furthermore, the rejection of the natural science model assumes that all of the natural sciences adopt the same experimental approach. Of course, they do not. Hayes, therefore, argues that the dichotomy between the two types of research methods is not as great as it would appear. If you were to set up a study in which you wanted to explore people’s attitudes to animal experimentation, say, which approach – qualitative or quantitative – would you think is best?
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Because psychologists must study living participants, they must obey ethical rules as well as yp scientific rules. Great care is needed in the treath c sy ment of human participants because we can hurt people in very subtle ways. The rules that govern psychologists’ conduct during experiments have been set by governments, institutions or professional societies and all psychologists engaged in research must abide by them. ee
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Research with human participants In Europe, North America and elsewhere, research undertaken by hospitals and universities will have been vetted by an ethics committee, which decides on whether the proposed research meets the institution’s ethical criteria regarding the welfare of human and animal participants in scientific research. Various professional societies such as the British Psychological Society (2006) and American Psychological Association (2002) issue guidelines for the treatment of humans and animals participating in research. In some countries, data may also fall within the remit of a data protection Act which, in its most general
form, allows an individual access to any information held electronically about them and, in research, allows the participant control over the use of such material. The BPS lists a number of recommendations which its members should follow (British Psychological Society, 2006). These recommendations fall into the general categories of consent, deception, debriefing, withdrawal, confidentiality and protection of participants. In general terms, a psychologist must treat participants with respect and must have taken all conceivable and practicable precautions to ensure that participants are not harmed. Threats to health, well-being, values and dignity should be eliminated.
Informed consent An important part of any procedure designed to ensure the proper treatment of participants is informed consent. When possible, a psychologist should always inform the participant of the nature of the experiment and, having been told the detail of this research, the participant – if willing – will consent to take part. This represents informed consent. Of course, it is not always possible to secure informed consent because divulging all aspects of the experiment will influence the decisions, thoughts, feelings and behaviours of the participant. This is considered in more detail in the section on deception. Usually, the potential participant reads a written statement prepared by the researcher. This discloses aspects of the research that might affect a person’s willingness to participate in the study. The informed consent statement constitutes a contract between participant and researcher and is normally signed by both of them. Examples of these appear in Figure 2.3. If participants are children, informed consent should be obtained from parents or guardians. The issue of child participation in research is an interesting one because, as you will see in Chapter 12, a child begins to grasp concepts and understand abstract ideas at certain periods in its development. This is the principal reason why parents or guardians consent to their children’s participation on their behalf. A study from the University of Texas suggests that this is sensible because children often do not understand the purpose of an experiment or may not understand what confidentiality of a person’s data means (Hurley and Underwood, 2002). Although the children understand some aspects better than others, they may continue to extend their trust to the experimenter. As with healthy, normally developing child participants, if a child or an adult participant is mentally ill, is unable to communicate or is mentally retarded, then a parent, healthcare worker or guardian should be informed and consent obtained from disinterested independent advisers.
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ETHICS
Attitudes of Mental Illness Study Informed Consent Form Please read the following information carefully and before you sign this form please ask questions you may have about the ‘attitudes to mental illness’study and your participation in it. In this study you will be asked to rate your agreement/disagreement with a series of statements about mental illness, along a 7-point scale with 1 representing strong agreement and 7 representing strong disagreement. For example, if you strongly agreed with the statement ‘I think that all mental illness is biological in origin’, you would circle ‘1’. The study will take approximately 30 minutes to complete. I fully understand the nature of the ‘attitudes to mental illness study’, that my participation is voluntary and that at any time I can terminate my participation without penalty. I am also aware that all my personal details and any information gathered about me will be kept confidential and will not be used for any purpose that is unrelated to the study. I understand that my data may be used to conduct analysis that may later be used for publication but that I will not be personally identifiable from these data
HIGHFLYER UNIVERSITY DEPARTMENT OF PSYCHOLOGY Psychology of Learning Experiment I confirm that I give my full and informed consent to participate in the above experiment. I understand that the information I provide will remain anonymous and disguised so that I may not be identified. I therefore give my permission for the results of this study to be published. (a) I understand that as part of this study I will be required to learn the works of Shakespeare. (b) I have been informed that the general aim of the study is to investigate learning strategies. (c) I have been informed that my general participation in this study will not involve unexpected discomforts or risks. (d) I have been informed that there are no disguised procedures in this experiment. The instructions can be taken at face value. (e) I understand that the experimenter will answer any questions that I have regarding the study once I have participated. (f) I understand that I am free to withdraw from the study at any time without penalty. Concerns about the study may be directed to the Chair of the Ethics Committee, School of Psychology, HighFlyer University Experimenter ____________________________ Date ________
Signed ________________ Date __________ (participant) Participant ______________________________
Date ________
Figure 2.3 (a) An example of a consent form used in research.
Figure 2.3 (b) A second example, suggested by R.J. Sternberg (1988a).
If a researcher is undertaking observational research then the privacy and psychological well-being of the participant must be accounted for. Unless consent to being observed is obtained, participants should normally be observed only under conditions where they would expect to be observed by strangers.
and actual nature of the experiment and to answer any questions that the participant may ask about the experiment. This is called debriefing.
Deception Psychologists are advised never to withhold information or mislead participants if an individual is likely to be uneasy when eventually told the purpose of the experiment. Sometimes, however, withholding information or using misleading information is necessary for good scientific reasons. When this occurs, it must be undertaken after obtaining the sound advice and approval of an ethics committee and colleagues.
Debriefing When participants take part in an experiment, the experimenter is obliged to disclose to the participant the real
Withdrawal If a participant feels that they have been unfairly misled or improperly treated, the participant has the absolute right to withdraw from the experiment. In fact, it should be made clear to all participants from the outset of the experiment that they are free to withdraw at any time, for whatever reason. The participant has the right to withdraw consent following the experiment or debriefing and request that their data be discarded or destroyed, or both.
Confidentiality Laws of the land notwithstanding, information and data provided by the participant in research are confidential. If data are published then those of individuals should not be identifiable, unless consent has been obtained.
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Protection of participants Tied to the recommendations concerning consent and deception are those governing the protection of the partici-
pant, which are very similar. Psychologists have a primary responsibility to their participants to avoid harm (physical or mental) and if harm is identified, to remove it.
Controversies in Psychological Science – Can research with animals help us to understand human behaviour? The issue Although most psychologists study the behaviour of humans, some study the behaviour of other animals. When we use another species of animal for our own purposes, we should be sure that what we are doing is both humane and worthwhile. Evidence suggests that whereas students regard the use of animals in medical testing as being warranted, they are less likely to agree that animals should be used in psychological experiments (Furnham and Heyes, 1993). Can animal research in psychology, therefore, be humane and worthwhile?
The evidence Humane treatment is a matter of procedure. We know how to maintain laboratory animals in good health in comfortable, sanitary conditions. For experiments that involve surgery, we know how to administer anaesthetics and analgesics so that animals do not suffer. Most industrially developed societies have strict regulations about the care of animals and require approval of the procedures that will be used in the experiments in which they participate. There is no excuse for mistreating animals in our care. In fact, the vast majority of laboratory animals are treated humanely because government departments ensure it. Whether an experiment is worthwhile is more difficult to say. We use animals for many purposes. We eat their meat and their eggs and drink their milk; we turn their hides into leather; we extract insulin and other hormones from their organs to treat people with diseases; we train them to do useful work on farms or to entertain us. These are all forms of exploitation. Even having a pet is a form of exploitation: it is we – not they – who decide that they will live in our homes. The fact is, we have been using other animals throughout the history of our species. Pet-owning causes much more suffering among animals than scientific research does. As Miller (1983) notes, pet owners are not required to receive permission to house their pets from boards of experts that include veterinarians, nor are they subject to periodic inspections to ensure that their homes are clean and sanitary, that their pets have enough space to exercise, and that their diets are appropriate. Scientific researchers are. Miller also notes that 50 times more
dogs and cats are killed by humane societies each year because they have been abandoned by their former owners than are used in scientific research. The use of animals in research and teaching is a special target of animal rights activists. Nicholl and Russell (1990) examined 21 books written by activists and calculated the number of pages devoted to concern for different uses of animals. Next, they compared the relative concern the authors showed for these uses to the numbers of animals involved in each of these categories. The authors showed relatively little concern for animals used for food, hunting or furs or for those killed in pounds. However, although only 0.3 per cent of the animals were used for research and education, 63.3 per cent of the pages were devoted to this use. In terms of pages per million animals used, the authors showed 665 times more concern for research and education than for food and 231 times more than for hunting. Even the use of animals for furs (which consumes two-thirds as many animals as research and education) attracted 41.9 times less attention per animal.
Conclusion Our species is beset by medical, mental and behavioural problems, many of which can be solved only through research involving animals. In fact, research with laboratory animals has produced important discoveries about the possible causes or potential treatments of neurological and mental disorders, including Parkinson’s disease, schizophrenia, manic-depressive illness, anxiety disorders, obsessivecompulsive disorders, anorexia nervosa, obesity and drug addictions. Although much progress has been made, these problems are still with us and cause much human suffering. Unless we continue our research with laboratory animals, these problems will not be solved. Some people have suggested that instead of using laboratory animals in our research, we could use tissue cultures or computer simulations. Unfortunately, tissue cultures or computer simulations are not substitutes for living organisms. We have no way to study behavioural problems such as addictions in tissue cultures, nor can we program a computer to simulate the workings of an animal’s nervous system. If we could, we would already have all the answers.
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CHAPTER REVIEW
Chapter review The scientific method in psychology • The scientific method allows us to determine the causes of natural phenomena.
• There are three basic forms of scientific research: naturalistic observations, experiments and correlational studies.
• Hypotheses are statements or predictions made on the basis
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of naturalistic observations, previous experiments or from formal theories. Psychologists might conduct experiments in which groups are independent of each other, the individuals in one group are not the same as those in the other (independent groups design); or experiments in which the same individuals take part in all conditions of the experiment (repeated measures design). An independent variable is an event, factor or action that is manipulated by the experimenter; the dependent variable is the quantity measured in an experiment (and is hypothesised to be influenced by the independent variable). To perform an experiment, a scientist alters the value of the independent variable and measures changes in the dependent variable. A psychologist must specify the particular operations that they will perform to manipulate the independent variable and to measure the dependent variable. Operational definitions are a necessary part of the procedure by which a hypothesis is tested; they can also eliminate confusion by giving concrete form to the hypothesis, making its meaning absolutely clear to other scientists. Validity is the degree to which an operational definition produces a particular value of an independent variable or measures the value of a dependent variable. Reliability refers to the consistency and precision of an operational definition. Researchers achieve high reliability by carefully controlling the conditions of their studies and by ensuring that procedures are followed correctly. Measurement involving subjectivity requires researchers to seek high interrater reliability. When designing an experiment, experimenters ensure that they control extraneous variables that may confound their results. If an extra variable is inadvertently manipulated and if this extra variable has an effect on the dependent variable, then the results of the experiment will be invalid. Confounding of subject variables can be caused by improperly assigning participants to groups or by treatments that cause some participants to leave the experiment. Most participants in psychological research try to guess what the experimenter is trying to accomplish, and their conclusions can affect their behaviour. If knowledge of the experimental condition could alter the participants’ behaviour, the experiment should be conducted with a single-blind procedure (where the
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participant is unaware of the condition they are in). If that knowledge might also alter the experimenter’s assessment of the participants’ behaviour, a double-blind procedure should be used (where the participant and experimenter are unaware of the condition that the participant is in). Correlational studies involve assessing relations among variables that the researcher cannot readily manipulate, such as personality characteristics, age and sex. The investigator attempts to hold these variables constant by matching members in each of the groups on all relevant variables except for the one being studied. Correlational studies cannot determine which variable is the cause and which is the effect. Single-subject research consists of the detailed observation of individual participants under different conditions. Case studies involve careful observations of the behaviour of specific people, such as those with psychological or neurological disorders. Researchers are seldom interested only in the particular participants they study; they want to be able to generalise their results to a larger population. The confidence that researchers can have in their generalisations depends on the nature of the variables being studied and on the composition of the sample group of participants. Qualitative analysis involves the examination of individuals’ expression of ideas, thoughts and feelings and is usually based on transcripts of discussion between individuals or between the experimenter and an individual/individuals.
Ethics • Because psychologists study living organisms, they must follow ethical principles in the treatment of their participants. Professional societies run by and for psychologists develop ethical guidelines that require informed consent, confidentiality and a post-experiment debriefing. • Participants may withdraw their consent to participate at any time before or during an experiment without any penalty. If deception is necessary, the experimenter must be certain that the participants will not be harmed psychologically or physically and that their dignity will be maintained. • Committees review all psychological research before giving their consent for it to be carried out to ensure that these guidelines are met. • Research that involves the use of laboratory animals is also guided by ethical principles. It is incumbent on all scientists using these animals to see that they are housed comfortably and treated humanely, and laws have been enacted to ensure that they are. Such research has already produced many benefits to humankind and promises to continue to do so.
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Suggestions for further reading Research methods: general reading There are many books about research methods, design and analysis available. Some of them you probably would not want to read – they aren’t the most riveting reads – but they serve a purpose in explaining how to do things. The best of research methods books, however, manage to engage you in the process of finding out how people behave. Some of these include the following: Bausell, R.B. (1993) Conducting Meaningful Experiments: 40 steps to becoming a scientist. London: Sage. Bausell’s short book is a very well-written, straightforward account of what you need to know and to do in order to become a scientist. It is laid out in the form of principles (40 of them) which the author describes, explains and illustrates. Foster, J.J. and Parker, I. (1995) Carrying Out Investigations in Psychology. Leicester: BPS Books. Another text which approaches research methods from the psychologist’s perspective and considers aspects of design not considered in more quantitative texts. Robson, C. (2002) Real World Research (2nd edn). Oxford: Blackwell. Robson’s excellent, well-written book delivers a comprehensive account of how to conduct ‘difficult’ research (i.e. out of the laboratory). Solso, R.L., Johnson, H.H. and Beal, M.K. (1998) Experimental Psychology (6th edn). Harlow: Longman. Solso et al.’s text provides a lot of very useful information about tracking down materials and writing up research as well as analysing some real, published research section by section.
Critical thinking Gabennesch, H. (2006) Critical thinking: What is it good for? Skeptical Inquirer, 30, 2, 36–41. Martin, G. N. (2009) Research and Study Update for Psychology (3rd edn). Harlow: Pearson Education. Matthies, B. (2005) The psychologist, the philosopher, and the librarian: The information-literacy version of CRITIC. Skeptical Inquirer, May/June, 49–52.
Meltzoff, J. (1998) Critical Thinking about Research: Psychology and related fields. Washington, DC: American Psychological Association. Melzoff’s is an extraordinary book because instead of analysing real research articles for quality, the author has composed several fictitious ones to highlight flaws in the ways in which studies are conducted, analysed and reported. The first half of the book is an excellent introduction to research methods; the second half consists of the research articles with a critical analysis of each. Superb for helping you develop critical thinking skills. The papers by Matthies and Gabennesch give some sound advice on critical thinking, as does the Martin title.
Qualitative research Smith, J.A. (2008) Qualitative Psychology (2nd edn). London: Sage. Willig, C. and Stainton-Rogers, W. (2008) The Sage Handbook of Qualitative Research in Psychology. London: Sage. Two relatively accessible texts on qualitative analysis.
Ethical issues in psychological testing Francis, R.D. (2009) Ethics for psychologists. Oxford: WileyBlackwell Gale, A. (1995) Ethical issues in psychological research. In A.M. Coleman (ed.), Psychological Research Methods and Statistics. London: Longman. Hurley, J.C. and Underwood, M.K. (2002) Children’s understanding of their research rights before and after debriefing: Informed assent, confidentiality and stopping participation. Child Development, 73, 132–43. Lindsay, G. (1996) Psychology as an ethical discipline and profession. European Psychologist, 1, 2, 79–88. Wilhelm, K. (2006) Do animals have feelings? Scientific American Mind, 17, 1, 24–9. Gale’s succinct chapter is a good introduction to ethics and psychological research. Lindsay’s article considers the ethical basis for the development of ‘ethical codes’ in psychology (such as those adopted by the British, American and European psychologists’ associations). Hurley and Underwood’s paper considers the implications of child development for obtaining ethical consent and for testing with children.
Journals to consult American Psychologist
Neurocase
Behavior Research, Instruments and Design
Psychological Bulletin
British Journal of Mathematical and Statistical Psychology
Psychological Methods
Current Directions in Psychological Science
Skeptical Inquirer
Educational Measurement and Assessment
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WEBSITE ADDRESSES
Website addresses http://www.apa.org/psycinfo/ http://wok.mimas.ac.uk/ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi/ http://www.csa.com http://cogprints.org/ http://www.psycline.org/journals/psycline.html A collection of links to resources in psychology, especially journals. Web of Knowledge (the second link) is particularly good. http://trochim.human.cornell.edu/tutorial/tutorial.htm http://www.socialresearchmethods.net/ http://davidmlane.com/hyperstat/ http://glass.ed.asu.edu/stats/ http://spsp.clarion.edu/RDE3/start/ A collection of links to sites and papers on research methods and statistics tutorials, including some online texts in research methods.
http://www.psychology.org/links/Resources/Doing_Research/ A good site with links to sites featuring basic information about doing research. http://psych.hanover.edu/research/exponnet.html This is a link to an enormous collection of online psychology experiments. Many psychologists are now conducting international and cross-cultural experiments in this way. http://psychexps.olemiss.edu/ http://epsych.msstate.edu/ http://kenstange.com/psycsite/ A few more links to online experiments and demonstrations in psychology. http://www.psychology.org/links/Resources/Ethical_Issues/ An excellent collection of links to sites on the psychology and ethics. http://www.badscience.net Ben Goldacre’s excellent debunking of pseudoscience and bad science reporting.
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Evolution, genetics and behaviour
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Science finds the secret of a hot kiss If you always thought you had a special chemistry with your loved one, you may finally have been proved right. Researchers have found that a passionate kiss unleashes a complex surge into the brain which makes a lover feel excited, happy or relaxed. There is also speculation that this hormone release may be triggered directly by an exchange of sexually stimulating pheromones in the saliva. [The] research looked at the impact of kissing on levels of two hormones, oxytocin and cortisol, in 15 male–female couples before and after holding hands and before and after kissing. Source: The Sunday Times, 8 February, 2009.
Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activities on: Chromosomes • Dominant and recessive traits • Twin studies and adoption studies of heritability • The inheritance of Huntington’s disease and Phenylketonuria • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 3
• Describe Darwin’s theory of evolution. • Outline the principles of genetic inheritance. • Evaluate the contribution of genetics to psychology. • Describe and evaluate sociobiology and evolutionary
• Discuss some of the reasons why we are sexually attracted to certain body types.
• Describe the psychological and evolutionary significance of altruism.
psychology’s contribution to our understanding of behaviour.
QUESTIONS TO THINK ABOUT
• What do you think is meant by the term ‘evolution of behaviour’?
• When did the modern human being evolve? • What are the implications of the theory of evolution for psychology?
• How do you think the process of evolution could explain modern behaviour such as romantic attraction, jealousy, language and marriage?
• Are we attracted to certain body types? If so, why?
• Why do you think that we have become more intelligent and sophisticated than our ancestors?
• What do you understand by the terms ‘genetics’ and ‘heredity’?
• Does culture or genetics have the greater influence on behaviour? Is the question an important one to ask?
• Are there any behaviours that can be unaffected by genetics?
• Why can we be altruistic and are we more altruistic to certain people than others?
CHAPTER 3
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The development of evolutionary theory From my early youth I have had the strongest desire to understand and explain whatever I observed, that is, to group all facts under some general laws. . . Therefore, my success as a man of science, whatever this may have amounted to, has been determined, as far as I can judge, by complex and diversified mental qualities and conditions. Of these, the most important have been – the love of science – unbounded patience in long reflecting over any subject – industry in observing and collecting facts – and a fair share of invention and common sense. With such moderate abilities as I possess, it is truly surprising that I should have influenced to a considerable extent the belief of scientific men on some important points. Source: Darwin, 1887, pp. 67–71.
These fairly humble words were written by a man who has influenced the course of scientific thought more than any other individual since Copernicus (who, in 1543, proposed that the sun, not the earth, was at the centre of the universe). Charles Darwin argued that, over time, organisms originate and become adapted to their environments by biological means. This concept is referred to as biological evolution – changes that take place in the genetic and physical characteristics of a population or group of organisms over time – and it stands as the primary explanation of the origin of life (Dawkins, 1986). The bicentenary of Darwin’s birth was marked in 2009, together with the 150th anniversary of the publication of one of the most important books published in the past 300 years – On the Origin of Species by Means of Natural Selection. In this book, Darwin distilled his theory of evolution. There is evidence of life on earth a billion years after the formation of the earth 4.5 billion years ago (Eiler, 2007) and the human race has existed, in various forms, for over 10 million years. This time-span has seen a tremendous change in our physical appearance, our biology and our behaviour. Our brains have developed, our societies have become more sophisticated, our intelligence has increased, our ability to communicate has improved, we have developed language systems. These processes illustrate the ways in which we have evolved and evolutionary theory seeks to explain why we have evolved in the way that we have. Why do birds have wings, giraffes have long necks, humans have bigger brains than other higher primates? How do changes in organic structure
occur and how does this happen? The answers to questions such as these have important implications for the topics discussed in other chapters in this book: intelligence, personality, social interaction, the use of language, the perception and expression of emotion, sex, hunger, mental disorder and so on. Although it has its roots in biology, Darwin’s work transcends biology and has influenced all the natural sciences, especially psychology (Dewsbury, 2009). In fact, Darwin himself had some aspirations for the young science. He wrote in 1859. In the distant future, I see open fields for more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history.
Since the 1970s, some psychologists have become increasingly aware of the various ways in which biology can influence behaviour. As you will see later in the chapter, many behavioural differences among organisms, both within and across species, correspond to genetic and other biological differences. Understanding these differences and their evolution allows psychologists to understand behaviour in terms of its possible origins and adaptive significance – its effectiveness in aiding the organism to adapt to changing environmental conditions. For example, gregariousness is the tendency to form groups or to be sociable; people tend to form social units. We live in families, have circles of friends, and join groups, such as churches, clubs or professional or recreational societies and political organisations. To understand the adaptive significance of gregariousness, we need to consider two questions. First, what events and conditions in a person’s lifetime might contribute to an individual’s gregariousness – what function does gregariousness serve in helping people adapt to the changing circumstances of life? Secondly, what events and conditions in the evolution of our species favoured gregariousness – what functions has gregariousness served in the history of humankind? These are important questions because a complete understanding of gregariousness, like any behaviour, requires that we understand both the past and present conditions that influence it. In other words, psychologists might research how past environmental conditions favoured gregariousness over a more solitary existence as a means of organising human culture and how the immediate environment influenced day-to-day sociability. They are interested in understanding both ultimate causes (from the Latin ultimatus, ‘to come to an end’) of behaviour – events and conditions that, over successive generations, have slowly shaped the
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behaviour of our species – and proximate causes (from the Latin proximus, ‘near’), namely immediate environmental variables that affect behaviour. By understanding how adaptive behaviour developed through the long-term process of evolution, psychologists are able to gain a more thorough understanding of our ability to adjust to changes in our immediate environment. To understand the present, we must understand the past – the history of the individual and the history of our species. We behave as we do because we are members of the human species – an ultimate cause – and because we have learned to act in special ways – a proximate cause. Both biology and environment contribute to our personal development. Relatively recently, a field of psychology has emerged, evolutionary psychology (Tooby and Cosmides, 1989; Buss, 1995), which attempts to describe and explain how an organism’s evolutionary history contributes to the behaviour patterns and cognitive strategies it uses for reproduction and survival during its lifetime. Evolutionary psychology’s contribution to our understanding of human behaviour is assessed later in the chapter. First, however, we describe Darwin’s theory of evolution. An understanding of this complex theory will help shed light on how behaviour has been interpreted, by some psychologists, in terms of evolution.
In the beginning: the voyage of the Beagle The story of how Charles Darwin developed his theory illustrates the mix of hard work, intellect and good fortune that often makes scientific discovery possible. In fact, Darwin’s work is an excellent example of how observation and experimentation can lead to scientific breakthroughs. After receiving a degree in theology from the University of Cambridge, England, in 1831, Darwin met a Captain Robert FitzRoy who was looking for someone to serve as an unpaid naturalist and travelling companion during a fiveyear voyage on board HMS Beagle. The Beagle’s mission was to explore and survey the coast of South America and to make longitudinal measurements worldwide. During the voyage, Darwin observed the flora and fauna of South America, Australia, South Africa and the islands of the Pacific, South Atlantic and Indian Oceans. He collected creatures and objects of every sort: marine animals, reptiles, amphibians, land mammals, birds, insects, plants, rocks, minerals, fossils and seashells. These specimens, which were sent back to England at various stages of the trip, were later examined by naturalists from all over Europe. Darwin did not form his theory of evolution while at sea. Although he was impressed by the tremendous amount of diversity among seemingly related animals, he believed in creationism, the view that all living things were designed by God and are non-evolving (Gould, 1985).
Charles Darwin (1809–82). Source: Northwind Photo Library.
The Origin of Species Upon his return home to England in 1836, Darwin continued to marvel at the many ways animals and plants adapt to their environments. He sifted through his collections, often discussing his findings and ideas with other scientists. He carefully reviewed the work of earlier naturalists who had developed their own theories on evolution. Darwin was not the first person to propose a theory of evolution, but he was the first to amass considerable evidence in its favour. He became interested in artificial selection, a procedure in which particular animals are mated to produce offspring that possess desirable characteristics. For example, if a farmer wished to develop cattle that yielded the largest steaks, then they would examine the available breeding stock and permit only the ‘beefiest’ ones to reproduce. If this process is repeated over many generations of animals, the cattle should become beefier. In other words, in artificial selection, people select which animals will breed and which will not based on specific, desirable characteristics of the animals. As he pondered on whether there might be a natural process corresponding to the role that humans play in artificial selection, Darwin’s views on evolution began slowly to change. He believed that ‘selection was the keystone of man’s success in making useful races of animals and plants. But how selection could be applied to organisms living in a state of nature remained for some time a mystery to me’ (Darwin, 1887, p. 53). A year-and-a-half later, on reading Malthus’s Population, Darwin proposed that because the ‘struggle for existence’ continued in plants and animals, then
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favourable variations would be preserved and unfavourable ones would die out. The result of such ‘selection’ would be the development of new species (Darwin, 1887). This proposal contains the idea of natural selection: within any given population, some members of a species will produce more offspring than will others. Any animal that possesses a characteristic that helps it to survive or adapt to changes in its environment is likely to live longer and to produce more offspring than are animals that do not have this characteristic. Darwin was well aware of the significance of his discovery but did not publish his theory until 20 years later, taking great pains to develop a clear, coherent and accurate case for his theory. Darwin might have been even slower in publishing his theory had it not been for an intriguing coincidence. In 1858, he received a manuscript from the Welshman, Alfred Russell Wallace, another naturalist, outlining a theory of natural selection identical to his own. Darwin’s colleagues suggested that he and Wallace make a joint presentation of their separate works before a learned society – the Linnean Society – so that each might lay equal claim to the theory of natural selection. This was done, and a year later Darwin published his ‘abstract’, which we know today as The Origin of Species. The book sold out on its first day of publication and has been selling steadily ever since. And although theories of evolution had existed before Darwin, he was the first to offer a systematic explanation for how evolution worked.
Natural selection and evolution Two concepts are central to Darwin’s theory of evolution: adaptation and natural selection. Adaptation refers to the ability of generations of species to adapt effectively to changes in the environment. Natural selection refers to the process whereby some variations in species will be transferred from one generation to the next but others will not. The Oxford zoologist, Richard Dawkins, has likened the process of natural selection to a sieve because it leaves out what is unimportant (Dawkins, 1996). Darwin’s theory has four basic premises:
1 The world’s animal and plant communities are dynamic, not static: they change over time with new forms originating and others becoming extinct. 2 The evolutionary process is gradual and continuous. New species arise through slow and steady environmental changes that gradually ‘perfect’ each species to its surroundings. When sudden and dramatic changes occur in the environment, a species’ ability to adapt is usually challenged. Some species adapt and live; others become extinct.
3 All organisms are descended from an original and common ancestor. Over time, the process of natural selection has created different species, each specifically adapted to its ecological niche. 4 Natural selection not only causes changes within populations during changing environmental conditions but also acts to maintain the status quo under relatively constant environmental conditions. According to Jacob (1977), natural selection results from two characteristics of life. First, reproduction produces offspring that are slightly different from their parents. Secondly, interaction with a changing environment requires that living things adapt behaviourally to its vagaries, otherwise they will risk injury, illness or death. The interaction of these factors causes differential reproduction, and, ultimately, evolution. Evolution, in this sense, is a process that is strongly influenced by behavioural adaptations to changing environments (Buss et al., 1998).
Natural selection The essence of Malthus’s essay, which Darwin was reading when the idea of natural selection first occurred to him, was that the earth’s food supply grows more slowly than populations of living things. The resulting scarcity of food produces competition among animals, with the less fit individuals losing the struggle for life. For example, wolves who are agile are better able to capture prey than are slower packmates. Fast wolves will therefore tend to outlive and out-reproduce slower wolves. If a wolf’s tendency to run fast is a genetically controlled trait, it will be passed on to its offspring. These offspring will be more likely to catch prey and will therefore live longer and have more opportunities to reproduce. The ability of an individual to produce offspring defines that individual’s reproductive success – the number of viable offspring it produces relative to the number of viable offspring produced by other members of the same species. Contrary to popular interpretation, ‘survival of the fittest’ does not always mean survival of the most physically fit or of the strongest. The evolutionary ‘bottom line’ is not physical strength but reproductive success. Physical strength is only one factor that might contribute to such success. In humans, for example, good looks, charm and intelligence play an important role in an individual’s ability to attract a mate and reproduce. What is more, natural selection is not ‘intentional’. Giraffes did not grow long necks in order to eat leaves from trees, but those with longer necks who were able to reach the leaves successfully reproduced while the others died out. Two aspects of natural selection – variation and competition – are the critical factors that determine whether any particular animal and its offspring will enjoy reproductive success.
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Variation includes differences among members of a species, such as physical characteristics (size, strength or physiology) and behavioural characteristics (intelligence or sociability). What factors are responsible for these sorts of variation? First, an individual organism’s genetic make-up – or its genotype – differs from that of all other individuals (except in the case of identical twins). As a result of these genetic differences, an individual organism’s physical characteristics and behaviour, or its phenotype, also differs from that of every other individual. Every individual’s phenotype is produced by the interaction of its genotype with the environment. In essence, the genotype determines how much the environment can influence an organism’s development and behaviour. For instance, identical twins have exactly the same genotype. If they are separated at birth and one twin has a better diet than the other, their phenotypes will be different: the betterfed twin is likely to be taller and stronger. However, regardless of diet, neither twin will ever become extremely tall or very muscular if they do not possess the genes for tallness and muscularity. Likewise, neither twin will realise their full potential for tallness and muscularity if they do not eat a nourishing diet. In this example, both the genotype (the genes related to tallness and muscularity) and a favourable environment (a well-balanced, nourishing diet) must be present for either twin to reach their full growth potential. Phenotypes and the genotypes responsible for them may or may not be selected, depending on the particular advantage they confer. Consider, for example, the thirteen species of finch that Darwin discovered in the Galapagos Islands, located off the west coast of South America. A striking physical difference among these birds is beak size. Some finches have a small, thin beak phenotype and others have a large, thick beak phenotype. Birds having small, thin beaks feed on small seeds covered by weak shells, and birds having large, thick beaks feed on large seeds covered by tough shells. In a study that investigated the relationship between rainfall, food supply and finch population on one island, Grant (1986) discovered that the amount of rainfall and the size of the food supply directly affected the activit ee mortality of finches having certain kinds of beak. During droughts, small seeds became yp sych scarce. As a result, the finches having small, thin beaks died at a higher rate than finches having bigger, thicker beaks. During the next few years, the number of finches having bigger, thicker beaks increased – just as the principle of natural selection would predict. During times of plentiful rain, small seeds became abundant, and the number of finches having small, thin beaks became more plentiful in subsequent years.
Grant’s study makes two important points. First, although evolution occurs over the long run, natural selection can produce important changes in the short run – in the space of only a few years. Secondly, phenotypic variation, in this case differences in beak size, can produce important selective advantages that affect survival. Imagine if all the finches had small, thin beaks: during the drought, most, if not all, of these finches might have died. None would be left to reproduce and these finches would have become extinct on this island. Fortunately, there was phenotypic variation in beak size among the finches, and because phenotypic variation is caused by genetic variation (different genotypes give rise to different phenotypes), some finches – those having large, thick beaks – had an advantage. Their food supply (the larger seeds) was relatively unaffected by the drought, enabling them to out-survive and out-reproduce the finches with small, thin beaks. On the basis of this evidence, one might reasonably assume that all finches should have developed large, thick beaks. However, when rain is plentiful and small seeds are abundant, birds with small, thin beaks find it easier to feed. Under these environmental conditions, these birds have a phenotypic (and genotypic) advantage.
Competition The second aspect of natural selection is competition. Individuals of a given species share a similar environment. Because of this, competition within a species for food, mates and territory is inevitable. Every fish captured and eaten by one bald eagle is a fish that cannot be captured and eaten by another bald eagle. If one bald eagle finds a suitable mate, then there is one fewer potential mates for other bald eagles and so on. Competition also occurs between species when members of different species vie for similar ecological resources, such as food and territory. For example, yellow-headed blackbirds and red-winged blackbirds eat the same foods and occupy the same types of breeding territory; thus, they compete for these resources. Such competition does not involve competition for mates (yellow-headed blackbirds do not court red-winged blackbirds and vice versa). However, although these species do not compete for mates, their competition for other resources indirectly influences reproductive success because the ability to find and court a suitable mate depends on the ability to stake out and defend a territory having an adequate food supply. The probability of a yellow-headed blackbird finding a mate and successfully rearing a family depends not only on its success in competing against other yellow-headed blackbirds, but also on its success in competing against red-winged blackbirds. Natural selection works because the members of any species have different phenotypes. Because these phenotypes
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are caused by different genotypes, successful individuals will pass on their genes to the next generation. Over time, competition for food and other resources will allow only the best-adapted phenotypes (and their corresponding genotypes) to survive, thereby producing evolutionary change. This is what the theory would predict.
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How widespread do you think the acceptance of the theory of evolution is? In the United States, it is law that science and religion are taught separately and that banning the teaching of evolution is unconstitutional (Scott and Matzke, 2007). In 2007, the Council of Europe’s Parliamentary Assembly passed a resolution recommending that member states do not teach creationism as if it were the equivalent of science. One survey of over a thousand students at a large American university, however, found that 25 per cent reported that their biology teacher had taught them creationism and 20 per cent were taught neither biology nor creationism (Moore, 2007). Creationism – the rejection of the theory of evolution in favour of the belief that the world was originated by a Creator – has gained some momentum in the US, although recent legal rulings suggest that evolution is fighting back. Creationism’s new incarnation is Intelligent Design but, to all intents and purposes, the terms are synonymous. The fierce and often acrimonious debate that exists between scientists and intelligent design advocates – see Dawkins’s excoriating The God Delusion – could probably make a Controversies in Psychological Science section in itself. Since 1985, American adults at various time intervals have been asked if the following statement is true or false: ‘Human beings, as we know them, developed from earlier species of animals’. In 2002, US data were compared with those from 9 European countries, with 32 countries in 2005 and with a survey of Japanese respondents in 2001 (Miller et al., 2006). Figure 3.1 illustrates agreement/disagreement with the statement by nation. Miller et al. found that over 20 years the percentage of Americans agreeing with the statement fell from 45 per cent to 40 per cent. Those who completely rejected the statement also fell from 48 per cent to 39 per cent. Those who were unsure jumped from 7 per cent in 1985 to 21 per cent in 2005. In later surveys, respondents were given the option of responding in a different way. They were asked whether the statement was definitely true, probably true, probably false, definitely false or don’t know. A third of Americans considered the statement to be false and only 14 per cent regarded it as definitely true. European and Japanese respondents were more likely to accept the statement as true. In fact, the only country which was more sceptical than the US was Turkey. Eighty per cent of Iceland, Denmark, Sweden and France agreed; 78 per cent of the
Germany (1507) Italy (1006) Netherlands (1005) Hungary (1000) Luxembourg (518) Ireland (1008) Slovenia (1061) Finland (1006) Czech Republic (1037) Estonia (1000) Portugal (1009) Malta (500) Switzerland (999) Slovak Republic (1241) Poland (999) Austria (1034) Croatia (1000) Romania (1005) Greece (1000) Bulgaria (1008) Lithuania (1003) Latvia (1034) Cyprus (505) United States (1484) Turkey (1005) 0
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Figure 3.1 This graph shows 34 nations’ degree of agreement with the statement ‘Human beings, as we know them, developed from earlier species of animals’. The survey was undertaken in 2005. Source: Miller, J.D., Scott, E. & Okamoto, S. (2006) Public acceptance of evolution. Science, 313, 765–6. Reprinted with permission from AAAS.
Japanese did. In European countries, the percentage absolutely disagreeing ranged from 7 per cent (Denmark, France, United Kingdom) to 15 per cent (The Netherlands). Those who strongly believed in God, who prayed often and held pro-life beliefs were the most rejecting of the statement. All of these were more common in the US. Miller et al. explains the geographic disparity by suggesting that biblical fundamentalism – Genesis is to be read literally – is greater in the US, whereas in Europe Genesis is regarded as being more of a metaphor. A third of US
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respondents also agreed that half of the genes of mice and humans are identical and 38 per cent believed that we have half in common with chimps (as you’ll see later, the percentage we share is a lot higher). Even if respondents disagreed with evolution, you might expect them to have a reasonable knowledge of the building blocks of life. Fewer than half of Americans surveyed were able to provide a passable definition of DNA.
Human evolution Reconstruction of human evolution is a difficult job, something akin to assembling a giant jigsaw puzzle whose pieces have been scattered throughout the world. Some of the pieces may have been lost for ever; others have become damaged beyond recognition; and those few that are found force continual reinterpretation of how the other pieces might fit the puzzle. Another way in which we can date our remains is via carbon dating. Animals breathe a form of (naturally occurring) radioactive carbon called C14. When an animal dies, this carbon decays but at a constant rate. By examining the content of the carbon in the fossil or surrounding material, therefore, we can estimate the date of its existence. One problem here is that the amount of carbon found can be influenced by the amount in the air at the time. We can also analyse the changes in DNA between similar fossils – the less the change in DNA, the closer the two fossils are in time. But the best we can do is make an educated guess about the evolution and lifestyles of our ancestors. Many biologists and natural historians of Darwin’s time believed that natural selection applied to all animals, including humans. Others insisted that although natural selection applied to other animals, it did not apply to humans. However, through study of the fossil record and recent developments in genetic research, we now know that our species is related genetically to other mammals. The gorilla and the chimpanzee are our closest living relatives, and together we appear to have descended from a common ancestor. You may have heard it said that we share 99 per cent of our genes with chimps. In fact, what we share is DNA involved in the production of proteins. Ninety-nine per cent of our DNA in this regard is identical (King and Wilson, 1975). Why, then, are we not exactly hirsute, whooping, tyre-swinging, banana-eaters? The reason is that 98 per cent of the human genome is not involved in the production of proteins. The remainder is involved in the timing of production and how much is produced (these are called regulatory genes – there is a more detailed description of genetics later in the chapter). It is this percentage which causes the great difference between the species (Demuth et al., 2006; Cohen, 2007). Humans also have multiple copies of genes that chimps
do not (Pennisi, 2006). Therefore, while we have proteins in common, it is the way in which these proteins are organised which determines the differences between us. Our dependence on information from fossil remains and other archaeological artefacts is problematic. As Byrne (1995) has colourfully pointed out, much of what we conclude about our ancestors’ behaviour from archaeological findings is speculative; some is sensible speculation but it is speculation nonetheless. There is no way of empirically or conclusively demonstrating that artefacts were used in the way in which we suggest or that they indicate a specific way of living or behaving. In this sense, paleoanthropology – the study of human behaviour using information from fossil remains – is more like detective work than scientific work. ‘The reality’, Byrne argues, ‘is that we will never know with confidence the answers to many of the most important questions we would like to ask about what happened in the past five million years’ (1995, p. 6). With this caveat in mind, the general pattern of evolution is thought to occur something like this. Our evolution from a common ancestor appears to have begun in Africa about 2 to 4 million years ago (Clark, 1993). The earliest humans have been labelled Homo habilis (literally ‘handy man’). Homo habilis was small (only about 1.3 m tall and about 40 kg in weight), but was bipedal (able to walk upright on two feet). Compared with its predecessor – a species called Australopithecus (‘apes from the South’) – Homo habilis had a larger brain and more powerful hands. The strong hands were well suited to making simple stone tools; hence the name ‘handy man’. A natural selection interpretation of such adaptively significant traits would argue that these early humans adapted to the environment in terms of creating shelter against the elements, catching and preparing food, and making weapons for self-defence. Homo habilis was succeeded, about 400,000 years later, by Homo erectus (‘upright man’). Homo erectus had a much larger brain and stood more erect than Homo habilis and had a more complex lifestyle. Homo erectus was the first of our ancestors to establish regular base camps, which probably served as centres for social activities, including the preparation and eating of food. We cannot be absolutely sure that these interpretations are the correct ones, however. Homo erectus created more efficient and stronger tools than did Homo habilis, successfully hunted big game, and discovered and used fire. Fire enabled these early humans to cook food, remain warm in cold weather and protect themselves from predators. Homo erectus’s use of fire, coupled with its apparent social nature and its ability to hunt and/or scavenge big game, permitted it to explore and settle new environments, including Europe, Asia, America and other parts of Africa (Spoor et al., 2007).
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The earliest known Homo sapiens (‘intelligent man’) appears to have arisen about 500,000 years ago. The best known of the early Homo sapiens, Homo sapiens neanderthalensis (so-called Neanderthals, named after the German valley in which the fossils were discovered), lived throughout Europe and Central Asia between approximately 300,000 and 35,000 years ago. Neanderthals constructed small huts from bones and animal skins and sometimes burned bones as fuel. They were skilled big game hunters, tool makers and clothiers, and they had cultural rituals for burying their dead. In one Neanderthal burial site unearthed in France, a small boy was found positioned on his left side with a small pillow of flints under his head and an axe positioned by his right hand. Similar Neanderthal burial sites have been discovered, suggesting that these humans possessed cultural traditions not previously found in the prehistoric record. Informed speculation suggests that Neanderthals and modern humans (Homo sapiens sapiens) overlapped each other, although the origin of Homo sapiens sapiens is unclear. It seems to have arisen between 200,000 and 100,000 years ago. The Neanderthals became extinct around 25,000 years ago, with last evidence of their existence found in Gibraltar (Finlayson et al., 2006). What is
clear, though, is that the Homo sapiens sapiens line has survived to flourish in all parts of the world, despite the presence of hostile climate, terrain and predators. Figure 3.2 charts the suspected development of Homo sapiens sapiens. Some theorists have suggested that the variety of species is greater nearer the equator (Hillebrand, 2004) and that tropical environments create a museum and a cradle for species to flourish (McKenna and Farrell, 2006).
Natural selection and human evolution The apparent success of the human species in adapting to a variety of ecological niches stems from the fact that natural selection has favoured two important human characteristics: bipedalism, the ability to move about the environment on two feet, and encephalisation, increased brain size. The ability to walk upright, which appears to have evolved in our early hominid ancestors over 4 million years ago (Boaz, 1993; Ruff et al., 1997), may have arisen from the need to stand on branches to reach food on other branches above (Thorpe et al., 2007). Bipedalism allowed not only greater mobility, but also freed the hands for grabbing, holding and throwing objects. The ability to grasp
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Figure 3.2 Major milestones in human evolution. The ability to walk upright freed the hands for tool use and other manipulative skills. Increased brain size accompanied increased intelligence. These two adaptations combined probably contributed significantly to all other major adaptations in human evolution. Source: Adapted from Lewin, R., Human Evolution: An illustrated introduction. Cambridge, MA: Blackwell Scientific Publications, Inc., 1984.
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objects, in combination with an expanding capacity for learning and remembering new skills provided by a larger brain, led to advances in tool making, food gathering, hunting and escaping predators (Eccles, 1989). Early hominids had a brain volume of 650 cm3 (and they were about 155cm tall). Current humans have a brain size of 1,500 cm3 and are, on average, 175 cm tall. It used to be thought that there was a relationship between body size and brain volume. However, the relationship is between relative size and brain volume and Figure 3.3 (a)–(c) shows the differences in brain and body size between various species. The increase in our brain relative to our size is called positive brain allometry. This began around 2 million years ago and has increased, more or less, since – from 450 cm3 (Homo habilis) to (a) H. neanderthalensis
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1,000 cm3 (Homo erectus) to 1,350 cm3 100,000 years ago (Homo sapiens). The increase may be attributable to better diet, better defence and, therefore, better survival. Children began to live longer, thus enabling the brain to be more fully developed when they conceived. As the brain became larger, more of its volume – especially the front part which is the most recently evolved – appeared to become devoted to thinking, reasoning, decision-making and other complex cognitive, ‘higher’ functions. We will return to the role of this part of the brain in thinking in Chapter 11. Another important ability that emerged from encephalisation was planning: the ability to anticipate future events and to consider the effects of these events on an individual or group of individuals. Such planning might have involved the organisation of hunts, the institution of social customs and events (such as weddings and funerals), and the planting and harvesting of crops. Over time, the interaction between bipedalism and encephalisation allowed humans to exploit new environments and establish well-organised communities. Advances in tool making and hunting, combined with the use of fire for cooking, protection and warmth, were adaptive: they helped humans to live longer. The increased lifespan of humans may have aided the gradual accumulation of wisdom as the older members of early
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Figure 3.3 These three figures show the relationship between brain size and body weight in our human ancestors and non-human primates (a); the weight of various species brains (b); and the relationship between body weight and brain size in a variety of different species (c). Source: Dicke, U. and Roth, G. (2008). Intelligence evolved. Scientific American Mind.
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human communities began to share their knowledge with younger members through language. Although the fossil record cannot tell us when language first developed, we assume that those who were able to communicate with others through language had a distinct advantage over those who could not. Language originated and subsequently evolved because of its immensely adaptive significance (Pinker, 1994). As Skinner (1986) noted, language not only provided a simple means of warning others of danger, but also provided a means of communicating important information to others, such as the location of a good hunting spot or instructions on how to craft a tool. Perhaps the most important advantage conferred by language was its ability to reinforce the already strong social tendencies of early humans. Language is the foundation upon which all human cultures are built and you’ll discover more about this in Chapter 10. As the evolution of cultures continued, humans gained an increasing ability to control and modify their environment. The same intellectual resourcefulness that permitted early humans to discover and use fire and to invent useful tools prompted the agricultural revolution of 10,000 years ago, the Industrial Revolution of 200 years ago, and the technological revolution that began only 50 years ago with the invention of the transistor, the integrated circuit and the computer. Cultural evolution, or the adaptive changes of cultures in response to changes in the environment over time, is possible only because humans have been genetically endowed with a capacity for learning and language. As cultural anthropologist Marvin Harris (1991) has noted, our capacity for learning has evolved because (1) it leads to ‘a more flexible and rapid method of achieving reproductive success’, and (2) it allows entire groups of people to ‘adjust or take advantage of novel opportunities in a single generation without having to wait for the appearance and spread of genetic mutations’ (p. 27). For example, advances in medicine have allowed us to control life-threatening diseases such as polio, smallpox, malaria, tetanus, typhoid fever and diphtheria. It would take hundreds of thousands of years, maybe even millions, to evolve immunities to these diseases. Curiously, however, evolution may have led to a genetic advantage in some which has made them more resistant to the human immunodeficiency virus or HIV. This is a fatal virus which attacks the immune system and leads to the illness autoimmune deficiency syndrome (AIDS). Today, 20 per cent of Southern Africans are infected with the virus. It was first reported around 50 years ago in Africa and, around 30 years later, cases appeared in the US and Europe. One theory for the appearance of the virus in humans may be that it invaded our system via ingestion. Monkeys contract a similar form called simian immune deficiency virus, but they appear resistant to it. This form of the virus was thought to be transferred to humans via
food – so-called bushmeat (from monkeys). Some humans, however, may also be resistant. Those who can trace their ancestry to northern Europe at the time of the plague might be beneficiaries of ancestors who were resistant to the bacterium that caused the plague (Galvani and Slatko, 2003). Both the plague and AIDS attack white blood cells. Around 10 per cent of the ancestors of these northern Europeans appear to have a copy of the gene which protected against the plague; 5 per cent of southern Europeans do, but no Africans do.
Heredity and genetics Darwin’s work unveiled the process of natural selection and created new frontiers for exploration and experimentation. One of the most important of these frontiers is genetics, the study of ‘the structure and function of genes and the way in which genes are passed from one generation to the next’ (Russell, 1992, p. 2). Genetics, then, also involves the study of how the genetic make-up of an organism influences its physical and behavioural characteristics. Related to genetics are the principles of heredity, the sum of the traits and tendencies inherited from a person’s parents and other biological ancestors. Although Darwin had built a strong case for natural selection, he could not explain a key tenet of his theory – inheritance.
The Brit, Francis Crick, and the American, John Watson, who cracked the DNA code and were rewarded with a Nobel Prize in 1962, jointly with Marcus Williams. Source: A. Barrington Brown/Science Photo Library Ltd.
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He knew that individual differences occurred within a given species and that those differences were subject to natural selection. But he did not know how adaptations were passed from parent to offspring. Six years after The Origin of Species was published, Gregor Mendel, an Austrian monk who conducted experimental cross-breeding studies with pea plants, uncovered the basic principles of heredity. Mendel demonstrated conclusively how height, flower colour, seed shape and other traits of pea plants could be transmitted from one generation to the next. His work has since been applied to studying heredity in thousands of plants and animals.
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Genes are segments of genetic material called DNA (deoxyribonucleic acid) – strands of sugar yp and phosphate that are connected by nucleotide h syc molecules of adenine, thymine, guanine and cytosine. Each pairs up with another, but guanine always pairs with cytosine and adenine with thymine. These pairs form steps in a spiral staircase called a double helix. That is, the DNA is configured like a twisted ladder: the sugar and phosphate form the sides and the four nucleotides form the rungs. You can see this in Figure 3.4. The particular sequence of these nucleotide molecules directs the synthesis of protein molecules that regulate the biological and physical development of the body and its organs. Some protein molecules regulate cell development and others regulate the chemical interactions that occur within cells. Three billion pairs of these proteins form our genetic code (Plomin, 2008). ee
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Protein synthesis Genes can only influence our development and behaviour through protein synthesis. Proteins are strings of amino acids arranged in a chain. Each sequence of nucleotides (adenine, thymine, guanine and cytosine) specifies a particular amino acid. In a sense, genes are ‘recipes’ consisting of different nucleotide sequences. In this case, the recipe is for combining the proteins necessary to create and develop physiological structures and for behaviour – how those structures might function in response to environmental stimulation. Strictly speaking, however, there are no genes for behaviour, only for the physical structures and physiological processes that are related to behaviour. For example, when we refer to a gene for schizophrenia (a mental disorder characterised by irrational thinking, delusions, hallucinations and perceptual distortions), we are really referring to a gene that contains instructions for synthesising particular proteins, which, in turn, are responsible for the development of specific physiological processes that are sensitive to certain stressful environmental conditions (we may even
Figure 3.4 The structure and composition of DNA. DNA resembles a twisted ladder whose sides are composed of molecules of sugar and phosphate and whose rungs are made of combinations of four nucleotide bases: adenine (A), thymine (T), guanine (G) and cytosine (C). Genes are segments of DNA that direct the synthesis of proteins and enzymes according to the particular sequences of nucleotide bases that they contain. In essence, genes serve as ‘recipes’ for the synthesis of these proteins and enzymes, which regulate the cellular and other physiological processes of the body, including those responsible for behaviour. Source: Based on Watson, J.D., Molecular Biology of the Gene. Menlo Park, CA: Benjamin, 1976.
be wrong in specifying just one gene – there may be more than one). The influence of genetics on mental disorders is discussed in more detail in Chapter 18. Genes also direct the synthesis of enzymes, proteins which govern the processes that occur within every cell in the body, and thus control each cell’s structure and func-
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tion. As we will see later, a faulty gene may contain instructions for synthesis of faulty enzymes, which produces serious physiological and behavioural problems.
depends on which type of sperm fertilises the ovum. A Ybearing sperm produces a boy, and an X-bearing sperm produces a girl. Figure 3.5(a) illustrates this process; Figure 3.5(b) shows the human chromosomes.
Chromosomes and meiosis Genes are located on chromosomes, the rod-like structures made of DNA found in the nucleus of every cell. In essence, genes are particular regions of chromosomes that contain the recipes for particular proteins. Each set of chromosomes contains a different sequence of genes. We inherit 23 individual chromosomes from each of our parents, giving us 23 pairs – 46 individual chromosomes – in most cells of the body. One pair of chromosomes, the sex chromosomes, contains the instructions for the development of male or female sex characteristics – those characteristics that distinguish males from females. Sexual reproduction involves the union of a sperm, which carries genetic instructions from the male, with an ovum (egg), which carries genetic instructions from the female. Sperms and ova differ from the other bodily cells in at least two important ways. First, new bodily cells are created by simple division of existing cells. Secondly, all 23 pairs of chromosomes divide in two, making copies of themselves. The copies pull apart, and the cell splits into two cells, each having a complete set of 23 pairs of chromosomes. Sperms and ova are formed by a special form of cell division called meiosis. The 23 pairs of chromosomes break apart into two groups, with one member of each pair joining one of the groups. The cell splits into two cells, each of which contains 23 individual chromosomes. The assignment of the members of each pair of chromosomes to a particular group is a random process; thus, a single individual can produce 223 (8,388,608) different ova or sperms. Although brothers and sisters may resemble each other, they are not exact copies. Because the union of a particular sperm with an ovum is apparently random, a couple can produce 8,388,608 8,388,608, or 70,368,774,177,664 different children. Only identical twins are genetically identical. Identical twins occur when a fertilised ovum divides, giving rise to two identical individuals. Fraternal twins are no more similar than any two siblings. They occur when a woman produces two ova, both of which are fertilised (by different sperms). Sex is determined by the twenty-third pair of chromosomes: the sex chromosomes. There are two different kinds of sex chromosomes, X chromosomes and Y chromosomes. Females have a pair of X chromosomes (XX); males have one of each type (XY). Because women’s cells contain only X chromosomes, each of their ova contains a single X chromosome (along with 22 other single chromosomes). Because men’s cells contain both an X chromosome and a Y chromosome, half of the sperm they produce contain an X chromosome and half contain a Y chromosome. Thus, the sex of a couple’s offspring
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Figure 3.5 (a) Determination of sex: the sex of human offspring depends on whether the sperm that fertilises the ovum carries an X or a Y chromosome. (b) Human chromosomes: the presence of a Y chromosome indicates that this sample came from a male. A sample from a female would include two X chromosomes. Source: CNRI/Science Photo Library Ltd.
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Dominant and recessive alleles activit
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Each pair of chromosomes contains pairs of genes: one gene in each pair is contributed by yp each parent. Individual genes in each pair can be h c sy identical or different. Alternative forms of genes are called alleles (from the Greek allos, ‘other’). Consider eye colour, for example. The pigment found in the iris of the eye is produced by a particular gene. If parents each contribute the same allele for eye colour to their child, the gene combination is called homozygous (from the Greek homo, ‘same’, and zygon, ‘yolk’). However, if the parents contribute different alleles, the gene combination is said to be heterozygous (from the Greek hetero, ‘different’). Heterozygous gene combinations produce phenotypes controlled by the dominant allele – the allele that has a more powerful influence on the expression of the trait. The allele for brown eyes is dominant. When a child inherits the allele for brown eye colour from one parent and the allele for blue eye colour from the other parent, the child will have brown eyes. Brown eye colour is said to be a dominant trait. The blue eye colour controlled by the recessive allele – the allele that has a weaker effect on the expression of a trait – is not expressed. Only if both of a child’s alleles for eye colour are of the blue type will the child have blue eyes. Thus, having blue eyes is said to be a recessive trait. Inheritance of two alleles for brown eyes will, of course, result in brown eyes. You can see this in Figure 3.6. Other eye colours, such as hazel or black, are produced by the effects of other genes, which influence the dominant brown allele to code for more (black) or less (hazel) pigment in the iris. It is important to remember that the genetic contributions to our personal development and behaviour are extremely complex. One reason for this complexity is that protein synthesis is often under polygenic control, that is, it is influenced by many pairs of genes, not just a single pair. The inheritance of behaviour is even more complicated, because different environments influence the expression of polygenic traits. Consider, for example, the ability to run. Running speed for any individual is the joint product of genetic factors that produce proteins for muscle, bone, blood, oxygen metabolism and motor coordination (to name but a few) and environmental factors such as exercise patterns, age, nutrition, accidents and so on. ee
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Genetic diversity No two individuals, except identical twins, are genetically identical. Such genetic diversity is a characteristic of all species that reproduce sexually. Some organisms, however, reproduce asexually, such as yeast and fungi. Nurseries often reproduce plants and trees through grafting, which is an asexual process. But when we examine
the world around us, we find that the overwhelming majority of species reproduce sexually. Why? One answer is that sexual reproduction increases a species’ ability to adapt to environmental changes. Sexual reproduction leads to genetic diversity, and genetically diverse species have a better chance of adapting to a changing environment. When the environment changes, some members of a genetically diverse species may have genes that enable them to survive in the new environment. These genes manufacture proteins that give rise to physical structures, physiological processes, and, ultimately, adaptively significant behaviour that can withstand particular changes in the environment. This reasoning explains why so many insects, such as cockroaches, have survived our species’ best efforts to exterminate them. The lifespan of insects is very short, so that even in a short period of time, many generations are born and die. When we attempt to alter their environment, as we do when we apply an insecticide to their habitat, we may kill many of them. However, some survive because they had the right combination of genes (and hence, the necessary physiological processes and behaviour patterns) to resist the toxic effects of the poison. The survivors then reproduce. Our reaction is to attempt to develop a new poison to which this generation of insects is not resistant. The result is a sort of evolutionary ‘arms race’ in which both insects and humans produce newer and more powerful adaptations in response to each other (Dawkins, 1986).
Influences of sex on heredity An individual’s sex plays a crucial role in influencing the expression of certain traits. A good example is haemophilia, an increased tendency to bleed seriously from even minor injuries. The blood of people who do not have haemophilia will begin to clot in the first few minutes after they sustain a cut. In contrast, the blood of people who have haemophilia may not do so for 30 minutes or even several hours. Haemophilia is caused by a recessive gene on the X chromosome that fails to produce a protein necessary for normal blood clotting. Because females have two X chromosomes, they can carry an allele for haemophilia but still have normal blood clotting if the other allele is normal. Males, however, have only a single X chromosome, which they receive from their mothers. If the gene for blood clotting carried on this chromosome is faulty, they develop haemophilia. The gene for haemophilia is an example of a sex-linked gene, so named because this gene resides only on the sex chromosomes. There are also sex-related genes that express themselves in both sexes, although the phenotype appears more frequently in one sex than in the other. These genes are called sex-influenced genes. For example, pattern baldness (thin hair across the top of the head)
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Figure 3.6 Patterns of inheritance for eye colour. (a) If one parent is homozygous for the dominant eye colour (BB), and the other parent is homozygous for the recessive eye colour (bb), then all their children will be heterozygous for eye colour (Bb) and will have brown eyes. (b) If one parent is heterozygous (Bb), and the other parent is homozygous recessive (bb), then their children will have a 50 per cent chance of being heterozygous (brown eyes) and a 50 per cent chance of being homozygous recessive (blue eyes). (c) If one parent is homozygous dominant (BB), and the other parent is heterozygous (Bb), then their children will have a 50 per cent chance of being homozygous for the dominant eye colour (BB) and will have brown eyes, and a 50 per cent chance of being heterozygous (Bb) for the trait and will have brown eyes. Source: Based on Klug, W.S. and Cummings, M.R., Concepts of Genetics (2nd edn). Glenview, IL: Scott, Foresman, 1986. © 1986 Scott, Foresman & Co. Reprinted by permission of Addison Wesley Educational Publishers, Inc.
develops in men if they inherit either or both alleles for baldness, but this trait is not seen in women, even when they inherit both alleles. The expression of pattern baldness is influenced by an individual’s sex hormones, which are different for men and women. The effects of these hormones on expression of pattern baldness explains why it is much more common among men than women. Sex-related chromosomes may be responsible for social cognition in humans (Skuse et al., 1997). Skuse and his colleagues examined a group of females aged between 6 and 25 years who had Turner’s syndrome. Turner’s syn-
drome is a genetic disorder in which all or part of one X chromosome in females is absent. These individuals are within the normal range of intelligence but they do have problems with social adjustment. In 70 per cent of Turner’s individuals, the remaining X chromosome is maternal in origin (Xm); in the rest it is paternal (Xp). Skuse and his group examined whether there were any differences between those individuals with an X chromosome that was maternal or paternal in origin. The researchers found that those with the maternally derived chromosome were less well adjusted than the 45,
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Xp individuals. The 45, Xm individuals were also less skilled in verbal ability and in reasoning, two functions which are essential to social cognition. The authors of the study suggest that these results indicate a genetic locus for social cognition. They also suggest that because the social cognition chromosome is derived from the father, this might explain why certain 46, XY males (whose X chromosome is derived from the mother) are more susceptible to developmental disorders such as autism (a disorder of social communication, language and emotion) than are 46, XX females. Developmental disorders such as autism are described in more detail in Chapter 12.
Mutations and chromosomal aberrations Changes in genetic material are caused by mutations or chromosomal aberrations. Mutations are accidental alterations in the DNA code within a single gene. Mutations are
the original source of genetic diversity. Although most mutations have harmful effects, some may produce characteristics that are beneficial in certain environments. Mutations can be either spontaneous, occurring naturally, or the result of human-made factors such as high-energy radiation. Haemophilia provides one of the most famous examples of mutation. Although haemophilia has appeared many times in human history, no other case of haemophilia has had as far-reaching effects as the spontaneous mutation that was passed among the royal families of nineteenth-century Europe. Through genealogical analysis, researchers have discovered that this particular mutant gene arose with Queen Victoria (1819–1901). She was the first in her family line to bear affected children – two female carriers and an afflicted son. The tradition that dictates that nobility marry only other nobility caused the mutant gene to spread rapidly throughout the royal families, as you can see from Figure 3.7.
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Figure 3.7 Genealogical analysis of the inheritance of haemophilia among European royal families. The gene for this disorder most likely originated with Queen Victoria of England. She was the first woman in the English royal family to bear an afflicted son or a carrier daughter. Circles represent females; squares represent males; a question mark indicates that carrier/afflicted status is unknown for that individual. Source: Adapted from Winchester, A.M., Genetics: A survey of the principles of heredity. Boston: Houghton-Mifflin, 1972.
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The second type of genetic change, chromosomal aberration, involves either changes in parts of chromosomes or a change in the total number of chromosomes. An example of a disorder caused by a chromosomal aberration – in this case, a partial deletion of the genetic material in chromosome 5 – is the cri-du-chat syndrome. Infants who have this syndrome have gastrointestinal and cardiac problems, are severely mentally retarded, and make crying sounds resembling a cat’s mewing (hence its name, ‘cry of the cat’). In general, the syndrome’s severity appears to be directly related to the amount of genetic material that is missing. Psychologists and developmental disability specialists have discovered that early special education training permits many individuals having this syndrome to learn self-care and communication skills. This fact highlights an important point about genetics and behaviour: even behaviour that has a genetic basis can often be modified through training or experience, a notion called epigenetics.
Epigenetics External events like trauma, drug abuse, lack of affection can affect the functioning of DNA. When these happen, the DNA does not alter, but is coated with molecules. These molecules alter the expression of the gene in two ways – either by preventing protein being constructed or by accelerating it. As you have seen, protein is essential to maintain the body and the brain. In the body, there is selective gene expression – each cell in the body may have the same gene but different cells use different types of gene. It does this via a molecule called ribonucleic acid (RNA), an intermediate molecule which is used by proteins attached to DNA to convert into other proteins. This is why a cell from the lung, for example, is different from one from the brain or the heart. A gene can be silenced; molecules can be prevented from accessing it and this is what epigenetic mechanisms do. They either facilitate or block access to the genes in cells. This, consequently, affects gene expression. In one experiment, the stress response of rats whose mothers had licked or groomed them consistently for up to 10 days after birth was compared with those who had not. The first group showed less anxiety and stress. The gene that allows the release of a hormone called corticosterone was examined in these pups and those who had not been licked had fewer corticosterone receptors in their brain (Meaney, 2004). One proposed mechanism for this is that the hormone interacts with a structure in the brain called the hypothalamus to prevent it from overreacting to stressful events.
A chromosome unravelled Source: Science Photo Library Ltd: Jacopin
Another protein, brain-derived neurotrophic factor (BDNF), which is important for the growth, integrity and functioning of cells, is lower in women with depression and it has been suggested that distressing events or experiences can alter the DNA that encodes this protein. In one experiment, ‘bully’ mice and smaller, normal mice were placed in a cage together for 5 minutes and then separated by a mesh for 10 days (Berton et al., 2006). As you might predict, the smaller mice showed the typical stress reaction – they would become submissive and anxious. However, when their brains were examined for levels of BDNF, these were lower in the bullied mice. More importantly, the molecule known to affect the expression of this protein was found in one region of the mice’s brains. This molecule had shut off the BDNF protein. A course of antidepressants raised the levels of BDNF. Similar to these genes are ‘knockout genes’, which work in a similar way. The animal is exposed to radiation which damages a gene. This inserts nucleotides in the gene which prevent it from expressing itself, hence, the gene has been ‘knocked out’. When the gene which encodes for spatial learning had been knocked out in rats, their ability to learn to swim to a platform that was not visible underneath a pool of water was impaired (Nakazawa, 2003).
Genetic disorders Many genes decrease an organism’s viability – its ability to survive. These ‘killer genes’ are actually quite common. On average, each of us has two to four of them. Fortunately, these lethal genes are usually recessive, and there are so many different types that most couples do not carry the same ones. When a child inherits the domi-
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nant healthy gene from one parent and the recessive lethal gene from the other, the destructive effects of the lethal gene are not expressed. A few lethal genetic disorders are caused by a dominant gene, however. Different dominant lethal genes express themselves at different times in the lifespan. A foetus may die and be spontaneously aborted before a woman even realises that she is pregnant; a baby may be stillborn, or the lethal genes may not be expressed until adulthood. There are many human genetic disorders. Those described below are some of the more common ones that impair mental functioning and behaviour and so are of special interest to psychologists.
lethal gene can be passed from parent to child before the parent even knows that he or she has the gene. The disease is rare (the prevalence is 2–7 individuals per 1,000) but because it is autosomal dominant, the child of a parent with Huntington’s disease has a 50 per cent chance of developing the disease. If the gene is present in the carrier, it will be expressed. There are genetic tests which help identify those individuals who carry the gene but this may present a horrible dilemma: if a person takes the test and is found not to carry the gene, then all well and good. If, however, the person is identified as a carrier, then this person will develop the disease and die from it because there is currently no cure. The Psychology in Action section describes some of the psychological consequences of this disclosure.
Down syndrome Down syndrome is caused by a chromosomal aberration consisting of an extra twenty-first chromosome (Simonoff et al., 1996). People having Down syndrome are generally short, have broad skulls and round faces, and show impaired physical, psychomotor and cognitive development. It occurs in around 1 in 1,000 births (DeGrouchy and Turleau, 1990) and about 15 per cent of children born with this condition die before their first birthday, usually from heart and respiratory complications. The frequency of Down syndrome increases with the age of the mother: about 40 per cent of all Down syndrome children are born to women over 40 years old. To a lesser extent, the age of the father also increases the chances of Down syndrome. Although people having Down syndrome are mentally retarded, special educational training permits many of them to hold jobs involving simple tasks. Despite the fact that Down syndrome is caused by a chromosomal aberration, it is not a hereditary disorder.
Huntington’s disease Huntington’s disease is a disorder of movement involving involuntary dance-like (choreiform), jerky movement. It does not emerge until the afflicted person is between 30 and 40 years old and is caused by a dominant lethal gene on the arm of chromosome 4 that results in degeneration in certain parts of the brain. Before the onset of this disease, an individual may be healthy in every respect. After onset, however, the individual experiences slow but progressive mental and physical deterioration, including loss of coordination and motor ability. Death generally occurs 5–15 years after onset. Because the age of onset for Huntington’s disease is long after sexual maturity, this
Phenylketonuria Individuals with phenylketonuria (PKU) are homozygous for a recessive gene on chromosome 12 responsible for synthesis of a faulty enzyme (called phenylalamine hydroxylase – around 500 mutations of the enzyme’s gene have been identified; see Widaman, 2009). This renders them unable to break down phenylalanine, an amino acid found in many foods. As a result, blood levels of phenylalanine increase, causing severe brain damage and mental retardation. Greater than 10 mg phenylalamine can be dangerous; a diet low in phenylalanine three weeks after birth can reduce this to between 3 and 10 mg. PKU is one of the many diseases for which infants are routinely tested before they leave the hospital. It occurs in 1 in 10,000–15,000 infants and those diagnosed as having PKU are placed on a low-phenylalanine diet shortly after birth. The disorder was originally reported by a Norwegian dentist who noticed that his two retarded children had a peculiar odour. This odour aggravated his asthma so badly that he could not stay in the same room with them (Plomin, 1997). Folling, the physician who examined the children, found excess amounts of phenylpyruvic acid in their urine because of disturbed phenylalanine metabolism. If diet is unrestricted, intellectual ability plummets and mental retardation can occur by the age of 2 (the child’s IQ would be around 50 or less, compared with the average 100). This decline is irreversible if there is no change in diet, which highlights the importance of altering diet quickly. Children who have been placed on a low phenylalanine diet for 20 years achieve normal development but if the diet is discontinued there is a drop in IQ performance (Koch et al., 2002). When the diet is restarted, the points are
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regained. It is estimated that for every mg of phenylalanine above 6.6, there is a 4.7 point loss in IQ (Koch et al., 2003). The mechanism for the illness is unclear but two candidates are the deficiency of a brain chemical called dopamine (described in the next chapter) or the slowing of myelination, the process whereby parts of a nerve cell are coated (this coating makes cells communicate more effectively) (Widaman, 2009).
Fragile X Fragile X is the most important cause of mental retardation after Down syndrome and is the most common inherited cause of mental retardation (Simonoff et al., 1996). It affects twice as many boys as girls (Kahkonen et al., 1987) and is so called because the X chromosome is fragile and easily broken. Children with fragile X tend to have large foreheads, prominent jaws and brow, and protruding ears.
Psychology in action – The psychological consequences of genetic counselling Genetic testing of susceptibility to disease has brought with it many remarkable psychological benefits, certainty and relief following a negative outcome being two of the more obvious. Positive outcomes appear to present an entirely different picture and one which may not be beneficial. Many anecdotal sources suggest that knowing the positive outcome of a genetic test for disease is associated with a decline in selfesteem and psychological well-being. There may also be health impairments that are unrelated to the disease. Couples having a family history of genetic disorders often seek genetic counselling, the process of determining the likelihood that a couple may produce a child having a genetic disorder. Individuals who suspect that they may have a genetic disorder may also seek such counselling. In women who might be carriers of the breast cancer gene (BRCA1/2), they do so for the sake of their children (d’Agincourt-Canning, 2006). Similar reasons, plus a feeling of responsibility to their families, are behind reasons for genetic testing for colon cancer and Huntington’s disease (Warner et al., 2006; Etchary, 2006). In instances where the woman is already pregnant, the foetus can be tested for genetic disorders. In fact, such testing is often recommended for pregnant women over 35 years of age or for those whose family pedigrees reveal a genetic problem. The most common prenatal detection method is amniocentesis, which involves removal and examination of foetal cells found in the amniotic fluid surrounding the foetus, usually during the sixteenth week of pregnancy. The chromosomes in the foetal cells are examined for incomplete, missing or extra chromosomes. In addition, amniocentesis allows parents to know the sex of their unborn child, which may be relevant in the case of sex-linked disorders. The first step in genetic counselling is generally a pedigree analysis of the family or families involved. This analysis identifies any family history of genetic disorders and provides an estimate of the likelihood that a genetic disorder is present. If
a family history of genetic disorders is discovered, the genetic counsellor discusses the probability of the couple having a child who has a disorder. In the case of an individual, the counsellor may recommend screening for the disorder. A group of researchers from the Netherlands (Tibben et al., 1997) examined levels of psychological distress in carriers and non-carriers of Huntington’s disease at four testing points: before knowing the results, one week after, six months after and three years after. They found that although helplessness increased in carriers and decreased in non-carriers at one week, the difference disappeared after six months. Those carriers with children reported greater distress than those without, and the partners of non-carriers were less distressed than those of carriers at three years. A study from the USA suggests a similar response but one which may be mediated by people’s approaches to coping with the illness (Codori et al., 1997). Codori et al. examined levels of hopelessness and depressive symptoms in patients tested positive for Huntington’s disease and those tested negative. They found that those who were least well adjusted were likely to have been positively diagnosed, were married with no children and were closer to their estimated age of onset. Men and women can differ in how they respond to the results of genetic testing (Marteau et al., 1997). Women carrying the cystic fibrosis gene mutation, for example, have been found to be more likely than men to be more relieved when told they were non-carriers but were also more likely to be less relieved than men when informed that they were carriers. These studies highlight a number of important questions in the area of genetic testing: which individual differences are risk factors for the anxiety and distress experienced following a positive test? Does the degree of distress change depending on the type of disease diagnosed? What are the long-term consequences of knowing the results of genetic testing? Studies such as those above present a fairly coherent beginning to finding answers to such questions.
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Each of us is born into a different environment and each of us possesses a unique combination of genetic instructions. As a result, we differ from one another. Consider your fellow undergraduates, for example. They come in different sizes and shapes, they vary in personality and intelligence, and they possess unequal artistic and athletic abilities. To what extent are these sorts of differences attributable to heredity or to the environment? If all your classmates had been reared in identical environments, any differences between them would necessarily be due to genetics. Conversely, if all your classmates had come from the same fertilised egg but were subsequently raised in different environments, any differences in their personal characteristics would necessarily be due only to the environment. Heritability is a statistical term that refers to the amount of variability in a trait in a given population that is due to genetic differences among the individuals in that population. Heritability is sometimes confused with inheritance, the tendency of a given trait to be passed from parent to individual offspring. But heritability does not apply to individuals, it pertains only to the variation of a trait in a specific population. The more that a trait in a given population is influenced by genetic factors, the greater its heritability. The scientific study of heritability – of the effects of genetic influences on behaviour – is called behaviour genetics. As noted by one of this field’s most prolific researchers, Robert Plomin, behaviour genetics is intimately involved with providing an explanation of why people differ (Plomin, 2008). As we will see below, behaviour geneticists attempt to account for the roles that both heredity and the environment play in individual differences in a wide variety of physical and mental abilities. The contribution of behaviour genetics to our understanding of the determinants of intelligence and personality are considered in more detail in Chapters 11 and 14. yp
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Studying genetic influences Although farmers and animal breeders had experimented with artificial selection for thousands of years, only within the past 150 years has the relation between heredity and behaviour been formally studied in the laboratory. Mendel’s careful analysis of genetic influences on specific characteristics gave us the first good clue that traits were actually heritable. As you saw in Chapter 1, Galton (1869) stimulated further interest in this field with his studies showing that intelligence tends to run in families: if parents are intelligent then, in general, so are their children. The search for genetic bases of behaviour has been active ever since. In fact, the search to understand the relative contributions of heredity and environment to human behaviour is among the most heavily researched areas in psychology.
Artificial selection in animals Any heritable trait can be selected in a breeding programme. The heritability of many traits in animals, such as aggression, docility, preference for alcohol, running speed, and mating behaviours, can be studied by means of artificial selection. Consider, for example, Tryon’s (1940) study of maze learning in rats. Tryon wished to determine whether genetic variables influenced learning. He began his study with a large sample of genetically diverse rats. He trained them to learn a maze and recorded the number of errors each rat made in the process. He then selected two groups of rats – those that learned the fastest (bright) and those that learned the slowest (dull). He mated ‘bright’ rats with other ‘bright’ rats and ‘dull’ rats with other ‘dull’ rats. To ensure that the rats were not somehow learning the maze from their mothers, he ‘adopted out’ some of the pups: some of the bright pups were reared by dull mothers and some of the dull pups were reared by bright mothers. He found that parenting made little difference in his results, so this factor can be discounted. Tryon continued this sequence of having rats learn the maze and selectively breeding the best with the best (bright) and the worst with the worst (dull) over many generations. Soon, the maze performance of each group was completely different. He concluded that maze learning in rats could be manipulated through artificial selection. Later studies showed that Tryon’s results were limited by the standard laboratory cage environment in which rats lived when they were not running the maze. For example, Cooper and Zubek (1958) demonstrated that differences in maze ability were virtually eliminated when bright and dull strains of rats were reared in either enriched environments designed to stimulate learning (cages containing geometric objects, such as tunnels, ramps and blocks) or impoverished environments designed to inhibit learning (cages containing only food and water dishes). However, Cooper and Zubek’s rats that were reared in the standard laboratory cage performed similarly to Tryon’s rats: the bright rats outperformed the dull rats. Thus, changing the environmental conditions in which the rats lived had an important result – reducing the effects of genetic differences between the bright and dull rats. This finding makes good sense when you consider the fact that genes are not expressed in the absence of an environment. Tryon’s research demonstrated that over successive generations a trait can be made to become more or less likely in a given population, but we do not know precisely why. We do not know whether genes related to learning or genes related to other traits were selected. Tryon’s rats may have been neither especially bright nor especially dull. Perhaps each of these strains differed in its capacity to be motivated by the food reward that awaited it at the end of the maze.
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Can gene manipulation ever occur in humans? Recent experiments involving the cloning of sheep illustrate the power of molecular genetics in radically altering nature’s forms. Gene mapping may help us to understand how specific DNA sequences can influence physiological processes that affect behaviour, emotion, remembering and thinking and play a crucial role in identifying specific genes involved in psychological disorders (Plomin and DeFries, 1998). Some of these issues are discussed in the chapters on memory, intelligence and mental disorders (Chapters 8, 11 and 18).
Twin studies There are two barriers to studying the effects of heredity on behavioural traits in humans. First, ethical considerations prevent psychologists and geneticists from manipulating people’s genetic history or restricting the type of environment in which they are reared. For example, we cannot artificially breed people to learn the extent to which shyness, extraversion or any other personality characteristics are inherited or deprive the offspring of intelligent people of a good education to see if their intelligence will be affected. Secondly, in most cases, the enormous variability in human environments effectively masks any correlation that might exist between genetics and trait expression. Psychologists have been able to circumvent these barriers by taking advantage of an important quirk of nature – multiple births. Recall that identical twins, also called monozygotic (MZ) twins, arise from a single fertilised ovum, called a zygote, that splits into two genetically identical cells. Fraternal or dizygotic (DZ) twins develop from the separate fertilisation of two ova. DZ twins are no more alike genetically than any two siblings. Because MZ twins are genetically identical, they should be more similar to one another in terms of their psychological characteristics (such as personality or intelligence) than either DZ twins or non-twin siblings (see Figure 3.8). Concordance research examines the degree of similarity in traits expressed between twins. Twins are concordant for a trait if both of them express it or if neither does, and they are discordant if only one expresses it. If concordance rates (which can range from 0 to 100 per cent) of any given trait are substantially higher for MZ twins than for DZ twins, heredity is likely involved in the expression of that trait. Table 3.1 compares concordance values between MZ and DZ twins for several traits. When we observe a trait exhibiting a high concordance for MZ twins but a low one for DZ twins, we can conclude that the trait may be strongly affected by genetics. This is especially true for a trait such as blood type, which has a heritability of 100 per cent. If the concordance rates are similar, the effect of heredity is low. For
Figure 3.8 Monozygotic twins. Source: Corbis: Outline.
example, consider the characteristic of religious beliefs. In this case, a high concordance value (that is, both twins having similar beliefs) probably reflects the fact that they acquired their beliefs from their parents. In fact, the concordance rate for religious beliefs of DZ twins is generally just as high as that of MZ twins (Loehlin and Nichols, 1976). Thus, religious beliefs are not inherited. Twin studies have been used to study a wide range of psychological phenomena. This research has shown that genetic factors affect cognitive abilities such as language ability, mathematical ability and vocabulary skills; personality traits such as extraversion (the tendency to be outgoing) and emotional stability; personality development; psychological disorders such as schizophrenia and mental retardation; and attitudes (Plomin et al., 1994b; Bouchard and Propping, 1993).
Table 3.1 Comparison of concordance rates between monozygotic (MZ) and dizygotic (DZ) twins for various traits
Trait Bood types Eye colour Mental retardation Measles Idiopathic epilepsy Schizophrenia Diabetes Identical allergy Tuberculosis
Concordance % MZ DZ 100 99 97 95 72 69 65 59 57
66 28 37 87 15 10 18 5 23
Source: Table 7.4, p. 161 from Concepts of Genetics, 2nd edn, by William S. Klug and Michael R. Cummings. Copyright © 1986 by Scott, Foresman and Company, Reprinted by permission of Pearson Education, Inc.
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Controversies in Psychological Science – Are attitudes genetically inherited? The issue Although social psychologists have explored why people hold the attitudes that they do, little research has considered the role of genetics in how these attitudes are formed. The general view is that our attitudes are shaped by our learning and by our experience. However, there are studies of dizygotic and monozygotic twins which suggest that pairs of identical twins hold more similar views on subjects such as religion, crime, punishment and so on than do pairs of dizygotic twins (Eaves et al., 1989).
The evidence In a study of the attitudes of 195 pairs of monozygotic twins and 141 pairs of dizygotic twins, Olson and his colleagues asked participants for their views on 30 diverse topics such as crossword puzzles, the death penalty for murder, sweets, immigration, loud music, making racial discrimination illegal, exercising and so on (Olson et al., 2001). Participants also rated themselves according to 20 personality traits, were asked how athletic, strong and physically attractive they thought they were and whether people considered them to be good-looking. The twins were recruited via newspaper advertisements. Identical twins were more likely to share similar attitudes on 26 of 30 attitude items than were dizygotic twins. Table 3.2 illustrates the concordance rates for the twins’ attitudes and personality traits. Does this suggest that there are genes for such attitudes? This is highly unlikely. Instead, the authors suggest that there may be more general traits of factors which reflect specific attitudes. For example, when they took personality into account, they found that the trait of sociability was highly associated with five of the six attitude factors, perhaps suggesting that sociability may be the underlying ‘cause’ of such attitudes and which may be the heritable factor. Participants’ attitudes towards leadership correlated with self-reported physical attractiveness, sociability and aggressiveness, but interpreting this relationship is difficult. For example, it could be argued that very attractive, sociable or aggressive people achieve leadership more easily and readily than do their less attractive, less sociable and less aggressive counterparts and that attitudes to leadership became more positive as a consequence. Conversely, participants may have been favourable towards leadership and made themselves more attractive, sociable or aggressive in order to achieve the status of leader. The researchers note that while their study showed a high degree of heritability of attitudes, the greatest predictor of variability in the attitude scores was variation in the experiences of individual pair members. For example, having a good football coach might make a physically able person more posi-
Table 3.2 Similarities in attitudes of monozygotic and dizygotic twins
Attitude Doing crossword puzzles Death penalty for murder Sweets Open-door immigration Doing athletic activities Voluntary euthanasia Smoking Being the centre of attention Separate roles for men and women Education Making racial discrimination illegal Loud music Getting along well with other people Capitalism Playing organised sports Big parties Playing chess Looking my best all the time Abortion on demand Public speaking Playing bingo Wearing clothes that draw attention Easy access to birth control Exercising Organised religion Being the leader of groups Reading books Castration as punishment for sex crimes Being assertive Roller coaster rides
MZ
Correlations DZ
0.46 0.45 0.36 0.47 0.41 0.45 0.49 0.31 0.27 0.30 0.37 0.53 0.20 0.41 0.52 0.44 0.38 0.42 0.53 0.34 0.37 0.38 0.24 0.35 0.43 0.40 0.55 0.39 0.28 0.50
0.11 0.33 0.23 0.20 0.26 0.21 0.38 0.14 0.26 0.14 –0.01 0.49 0.19 0.19 0.10 0.30 0.22 0.14 0.28 0.26 0.33 0.28 0.27 0.17 0.21 0.08 0.24 0.29 0.27 0.31
Source: Adapted from Olson, J.M., Vernon, P.A., Harris, J.A. and Jang, K.L. The heritability of attitudes: A study of twins. Journal of Personality and Social Psychology, 2001, 80(6) 845–60, copyright 2001 by the American Psychological Association, reprinted with permission.
tive about their physical strength and help them develop more positive attitudes towards sports; similarly, poor reinforcement from teachers or criticism of performance might lead to a child’s withdrawal into shyness and subsequent negative attitudes towards leadership.
Conclusion While there is a strong relationship between the attitudes of each of a pair of identical twins, there are events that both twins experience which could shape such attitudes.
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Sociobiology Sociobiology has been defined as ‘the systematic study of the biological basis of all social behaviour’ (Wilson, 1975). It represents the synthesis of research findings regarding social behaviour from many other fields of science, including those from evolutionary psychology, anthropology and behaviour genetics. Evolutionary psychology and behaviour genetics are more specific fields than sociobiology in the sense that both are concerned with phenomena such as intelligence and cognition, in addition to social behaviour. Sociobiologists are especially interested in understanding the evolutionary roots of our modern-day social actions. More often than not, sociobiologists study the evolutionary bases of social behaviour in non-human animals and then extrapolate from those species to humans (Barash, 1982). Sociobiology represents an interface between the biological sciences and psychology. However, not all psychologists are convinced of the sociobiologists’ claims, arguing that sociobiology is too simplistic and that its emphasis on genetics inadequately explains the complexities of human behaviour.
Reproductive strategies and the biological basis of parenting Perhaps the most important social behaviours related to the survival of a species are those related to reproduction and parenting. A focal point of sociobiological research and theory has been understanding more about the different kinds of social organisation that result from particular reproductive strategies – systems of mating and rearing offspring. We assume that most Western sexual relationships are monogamous: the mating of one female and one male. If mating is successful, the individuals share in the raising of the child or children. But monogamy is just one of several reproductive strategies sexual creatures employ in mating and rearing of offspring (Barash, 1982). Three other major classes of reproductive strategy are also possible:
• Polygyny: one male mates with more than one female. • Polyandry: one female mates with more than one male. • Polygynandry: several females mate with several males. Figure 3.9 illustrates the combinations of partners that give rise to these classes. According to Trivers (1972), these four reproductive strategies evolved because of important sex differences in the resources that parents invest in conceiving and rearing their offspring. Parental investment is the time, physical
Females
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Polygyny
One female
Polygynandry
Monogamy
One male
Polyandry
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Figure 3.9 Reproductive strategies. Different numbers of males mating with different numbers of females yields the four reproductive strategies of monogamy, polygyny, polyandry and polygynandry.
effort and risks to life involved in procreation and in the feeding, nurturing and protecting of offspring. According to sociobiologists, parental investment is a critical factor in mate selection. An individual who is willing and able to make a greater investment is generally more sought after as a mate and is often more selective or discriminating when selecting a mate (Trivers, 1972). Given that a human female will gestate for nine months, she should be highly selective about choosing a mate. On the basis of Trivers’s theory, it is possible to predict that women will express an (evolved) preference for men who have high status and will divorce those who do not contribute the expected resources or who divert them to other women and children (Buss, 1995). In some species, competition for mates leads to sexual selection – selection for traits specific to sex, such as body size or particular patterns of behaviour. For example, in some animals, such as buffalo, females select mates based on the male’s ability to survive the skirmishes of the rutting (mating) season. In general, the larger and more aggressive males win these battles and gain access to more females and enjoy greater reproductive success. Polygyny is by far the most common reproductive strategy among humans. Eighty-four per cent of human societies practise polygyny or allow men who are either wealthy or powerful to practise it (Badcock, 1991). Monogamy is the next most popular reproductive strategy, with about 15 per cent of all human cultures practising it. Polyandry and polygynandry are both rare: combined, these two reproductive strategies dominate in fewer than 1 per cent of all human cultures.
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Polygyny: high female and low male parental investment In many species, the female makes the greater parental investment. According to sociobiological theory, whether one is an ova producer or a sperm producer defines the nature of one’s parental investment. The fundamental asymmetry between the sexes has been aptly captured by sociobiologists Daly and Wilson (1978, p. 48):
Although each parent contributes almost equally to the genetic resources of the new creature they create, not all contributions are equitable. The female provides the raw materials for the early differentiation and growth of their progeny. Here at the very fundament of sexuality, is love’s labour divided, and it is the female who contributes the most.
Among most mammals (including humans), the costs associated with reproduction are higher for females than for males. First, females have fewer opportunities than males to reproduce. Generally, females produce only one ovum or a few ova periodically, whereas males produce vast quantities of sperm over substantially shorter time intervals. Secondly, females carry the fertilised ovum in their bodies during a long gestation period, continuously diverting a major portion of their own metabolic resources to nourish the rapidly growing foetus. Females also assume all the risks that accompany pregnancy and childbirth, including physical discomfort and possible death. The male’s contributions to reproduction are, at a minimum, the sperm and the time needed for intercourse. Thirdly, after the offspring is born, females may continue to devote some of their metabolic resources to the infant by nursing it. Just as important, they usually devote more time and physical energy than males to caring for the newborn. In addition, a female can only bear a certain number of offspring in a lifetime, regardless of the number of males with whom she mates. In contrast, a male is limited in his reproductive success only by the number of females he can impregnate. For example, consider the differences between females and males in our species. If a woman became pregnant once a year for ten years, she would have ten children – only a fraction of the number of children that a man is capable of fathering over the same interval. If a man impregnated a different woman every month for ten years, he would have fathered 120 children. This example is hardly an exaggeration. According to the Guinness Book of World Records, the largest number of live births to one woman is 69 (she had several multiple births). In contrast, King Ismail of Morocco is reported to have fathered 1,056 children.
In many polygynous species, intense competition for the opportunity to mate occurs among males. The competition almost always involves some sort of physical confrontation: that is, males fight among themselves for the opportunity to mate. Usually, the larger, stronger and more aggressive male wins, which means that only he will mate with the available females in the vicinity. If one of the smaller, weaker males attempts to mate with a female, he is generally chased away by the victorious male. Because females in polygynous species invest so heavily in their offspring, they are – according to sociobiologists – usually highly selective of their mates, choosing to mate only with those males who possess specific attributes, such as physical size, strength and aggressiveness. Such selectivity makes adaptive sense for both the female and her progeny. After all, bearing the offspring of the victor means that her male offspring will tend to possess the same adaptively significant attributes as their father and thus be more likely to win their own quests for mating privileges. And, as a result, genes for large size, increased strength and aggressiveness will continue to have greater representation in future generations than will genes for less adaptive attributes. The theory also works the other way – the male will select a female that he considers attractive and healthy and would, therefore, be a fit mother for a child. This interpretation, however, rests on the assumption that mate selection is governed by the perceived ability to reproduce successfully. In essence, it is, like the assumptions made about the evolution of our ancestors: speculative. This view does not explain why some couples decide to forgo the opportunity to have children. Physical attraction is also heavily culture-bound, as the International Perspective section shows.
Facial and bodily attractiveness As the International Perspective section below shows, some studies find that body mass index (BMI) is more important than shape to ratings of physical attractiveness, especially when full-frontal figures are rated. Shape may be more important if a figure is seen in profile. To test this hypothesis, Tovee and Cornelissen (2001) asked 40 male and 40 female undergraduates in the UK to rate a set of photographs of real women with obscured faces. The authors criticise previous studies for using unrealistic stimuli, such as (poor) line drawings of female figures presented in front view only, hence the use of real photographs and two views. There were 50 front-view figures and 50 in profile. BMI, not waist-to-hip ratio, was the best predictor of attractiveness for figures seen from the front or in profile. Both men and women gave similar ratings, thus supporting the second hypothesis, and both sexes preferred the figures with the lowest waist-to-hip ratio (a curvaceous figure).
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Physical attraction – An international perspective activit
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In the developed world, physically attractive women are considered to be those with a low waist-to-hip ratio (WHR); yp sych this WHR is achieved because more fat is deposited on the buttocks and hips than the waist (this, in turn, is the result of women having higher levels of oestrogen than testosterone) (Singh, 1995). This apparent universal preference for women with low WHR would seem to bolster the sociobiologist’s argument that mates are selected for their health and fitness. However, these preferences are not universal. Yu and Shepard (1998) compared the body shape preferences of American men and men from the Matsigenka people in south-east Peru. The Matsigenka’s culture is basically agrarian: they engage in slash and burn agriculture and supplement this food production with game and fruit gathered using traditional tools. Only scientists and official visitors are allowed to visit the village. The men had lived in the village since birth and would not, therefore, have been exposed to Western civilisation (no television, film, newspapers and so on). Whereas the Western sample predictably preferred those females with low WHR, the Matsigenka men preferred overweight females and those with high WHR, rating these as the more attractive, healthy and more desirable as a spouse. The authors repeated the experiment on two other groups living outside the Matsigenka’s village and who had been exposed to more Western influences. Here, the findings were mixed. One group showed the same pattern whereas the other gave comparable ratings to the Americans. These findings cannot be explained in terms of individuals selecting the fittest, most convincing-looking baby-producing machines. The nonWesternised group regarded a high WHR as healthier than a low WHR; the opposite effect was seen in the American group. In a similar study, Frank Marlowe and Adam Wetsman, two American anthropologists, presented a series of frontal drawings of women which varied in their WHR to the Hazda group of hunter-gatherers who inhabit mixed savannah woodland in Tanzania (Marlowe and Wetsman, 2001). A previous study had shown that the men in this group were more swayed by women’s weight than their WHR and strongly disliked thin women. In their new study, the images varied only by WHR, not weight. The group’s responses were compared with those of a group of American men. The researchers found that whereas the American men preferred a low WHR and especially liked the intermediate image showing a WHR of 0.7, the Hazda men preferred a higher WHR. The authors argue that this choice reflects a preference for heavier women and further speculate that ‘the more subsistence-oriented a society is, and the more energetically expansive women’s work, the more men will find fatter women attractive. Among foragers, thinness probably indicates poorer health.’ A study of physical attraction in Britain and Malaysia has found that participants in both countries consider body mass ee
index (BMI), weight adjusted for height (see Chapter 13 to see how you calculate this), to be a better index of female attractiveness than waist-to-hip ratio (Swami and Tovee, 2005a). The researchers asked 682 participants to rate the photographs of real women. The study found that those who lived in urban areas preferred lower BMIs than did those living in the country, perhaps reflecting the greater exposure of urbanites to slimmer women. Geographical differences were also found when British and Malaysian people rated photographs of men (Swami and Tovee, 2005b). People who lived in urban areas preferred men with low waist-to-chest ratio (BMI or waist-to-hip ratio were not good predictors). In rural areas, however, BMI was the primary predictor of attractiveness. Urban raters preferred a men with an ‘inverted triangle’ shaped torso, whereas rural raters preferred heavier men with a less triangular shape. Swami and colleagues have also reported an interaction between WHR and breast size. South African men preferred high-WHR black figures with large breasts and high-WHR white figures with small breasts, whereas white British men and British Africans preferred high-WHR black figures with small breasts and high-WHR white figures with large breasts (Swami et al., 2009).
Is women’s waist-to-hip ratio and men’s waist-to-chest ratio the key to physical attractiveness? Source: © Mitchell Gerber/Corbis.
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What this might suggest is that BMI and WHR reflect different aspects of female health and fitness. BMI may reflect general fitness and fertility whereas WHR is a ‘more specific cue to fertility and pubertal status’ although the authors acknowledge that this cue has its limitations. The WHR of anorexic and healthy women is similar, for example, although the anorexic group (which is amenorrheic, i.e. not menstruating) is not fertile whereas the healthy group is. The same research group has also investigated what makes the ideal male body shape (Maisey et al., 1999). They asked 30 female undergraduates to rate the attractiveness of 50 men. Each man was measured for waist-to-chest ratio (WCR), WHR and BMI. They found that the best predictor of a man’s attractiveness was his waist-to-chest ratio. Unlike men, who prefer a certain body size, women prefer a certain shape. This is the ‘inverted triangle’ (narrow waist, broad shoulders). The researchers suggest that if the desirable WHR in women signifies health and reproductive potential, then a desirable WCR in men signifies physical strength. The preference for the triangular shape in urban dwellers is probably influenced, in part, by the muscular quality that the shape presents. If men believe that a muscular body is attractive, then attaining a muscular torso should improve their body image. In a study where men and women engaged in a 12-week muscular training exercise programme, men who trained were significantly happier with their body image at the end than at the beginning (Ginis et al., 2005). Interestingly, this improvement correlated with physical improvements in strength in men but with both physical improvements and subjective ratings of physical improvement in women. Homosexual men also judge muscularity to be more important than weight when they rate their own attractiveness (Levesque and Vichesky, 2006). Men’s weight, however, can influence people’s judgement of their personality. Wade et al. (2007) found that thinner men were rated as more socially desirable than overweight men. Thin men and men of normal weight also received higher ratings for friendliness, trustworthiness, intelligence and mate potential. Bodies are often covered and we may not be able to perceive their exact shape; faces, however, are almost always exposed and offer an immediate source of information about physical attractiveness. Furnham et al. (2001) asked 100 young men to rate the images of women for attractiveness, sexiness, and health. The images had been morphed so that bodies varying in WHR either featured an attractive or unattractive face (as determined in a pilot study). Contrary to what one might expect, images with attractive faces were rated as healthier, sexier, more attractive and more fertile regardless of WHR. The evi-
dence is contrary to what we would expect from the ‘first pass filter’ theory of mate selection. This refers to the notion that WHR is the first feature we focus on to determine our attraction to a partner; if it is acceptable, we then focus on other features and behaviours to further refine our choice. People also find facial symmetry (where the left and right sides are almost totally symmetrical) attractive and healthy. Men with more symmetrical bodies have been reported to display more direct, sexual, competitive tactics when trying to win their date (Simpson et al., 1999) and symmetrical movers are judged to be significantly better dancers than are asymmetrical ones (Brown et al., 2005b). Of course, physical beauty is stereotypically (and selfevidently) skin-deep. A study by Swami et al. (2007) asked participants to rate line drawings of women which varied in body weight, waist-to-hip-ratio and personality (extravert, introvert). Extraverted ‘women’ were judged to be more attractive and sociable than introverted ones, indicating that non-physical features are also an important determinant of attractiveness.
The perils of being beautiful Is there a disadvantage to being very attractive? Research suggests that there is. When female students were asked to judge the suitability of an attractive, average and unattractive man as a long-term partner in tandem with a lonely heart advertisement implying high, medium or low socio-economic status, who do you think the women chose? If you said high-status, attractive men, you’d be wrong. If you’d said attractive men of medium status, you’d be right. Why? According to the authors (Chu et al., 2007) the women regarded attractive, high-status men as pursuing a mating strategy (simply put, they were after sex), rather than a parenting strategy (wanting to settle down). High-status, attractive men would, therefore, be far more likely to be the recipient of other women’s attention (and, therefore, be at greatest risk of yielding to this attention). Women – well, UK undergraduates – it seems, don’t want Mr Perfect, just Mr Almost Perfect. They might also settle for Mr Average. In one study women engaged in speed-dating were asked how important they thought a man’s physical attractiveness and earning prospects were (Eastwick and Finkel, 2008). In an ideal partner, these were considered to be important. However, this preference did not predict their mate choice at the dating evening, neither did it predict their choice of real-life partners when the researchers contacted them after the study. One theory of attractiveness (the topic of romantic attraction is considered further in Chapter 16) suggests that we choose a mate who is similar in attractiveness to
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ourselves (even if we prefer busty blondes or six-packed hunks). This is called the matching phenomenon (Walster et al., 1966), but no model can explain this satisfactorily – is it because we are more anxious or insecure, or fear rejection, or have low self-esteem? Some social psychologists argue that we view others through our own egotistical lens. ‘The self provides the frame of reference from which all else is observed’, state Combs and Snygg (1959), ‘People are not really fat unless they are fatter than we.’ This would suggest that our ratings of others’ physical attractiveness is affected by our assessment of our own physical attractiveness (whether this view is shared by others or not). Montoya (2008) found that people don’t seem to settle. In their study, participants’ ratings of
another person’s attractiveness decreased with the increasing, objective, physical attractiveness of the rater. People rating themselves moderate in attractiveness paired themselves with people they thought were attractive. There is support for his finding. A recent study found that people rated their partners as being significantly more attractive than themselves – there was no difference between men or women (Swami et al., 2009). Are these people deluding themselves? Or are we all physically attractive and beauty is in the eye of the beholder? Remember that these studies focused on physical attractiveness, not the attractiveness of a partner’s personality or outlook or love of cats or helping old ladies with their shopping. Why do you think these percentages are so high?
Cutting edge – Can I have your number? Can times of high and low fertility influence a woman’s acceptance of a romantic overture? Nicolas Guegen, from the University of Bretagne-Sud, set up an experiment in which a 20-year-old confederate approached women in a pedestrianised zone of the city of Vannes and said: ‘Hello. My name’s Antoine. I just want to say that I think you’re really pretty. I have to go to work this afternoon, and I was wondering if you would give me your phone number.’ (Guegen, 2008) He then waited for 10 seconds, gazed at his prey, smiled and waited for a response. Thirty to forty seconds after the woman departed, she was approached by a researcher who explained that the man was part of study and that they were interested in her responses to certain questions: 455 women participated. The preference for Gallic fromage aside, did women’s menstrual cycle influence their likelihood of accepting the overture? Yes, it did. Those in the fertile phase of their cycle were more likely to furnish their number, but only if they were not taking oral contraceptives. Guegen (2008) suggests that this might be explained by the fact that young French women are likely to use the pill when in a relationship, but stop when this ends. The combination of availability and high fertility may have led to the increased willingness to give a strange, attractive man their number. This research is one in a line of studies exploring the effects of point of menses on women’s feelings of sexual attractiveness. Women are judged to be more attractive when they are in the follicular stage of their cycle and men find their body odour more attractive. Women’s appetite decreases during ovulation. They also make themselves look more attractive during this period. For example, Haselton et al. (2007) asked men and women to judge the attractiveness of 30 women who had partners and who were in the luteal or follicular stage of their cycle. More women in the follicular stage were judged as ‘trying to
look more attractive’. The closer the women were to ovulation (when the photograph was taken), the more likely the photograph was chosen as signifying someone attractive. These women were judged to wear more fashionable clothes, nicer clothes and show more upper body skin.
(a)
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Figure 3.10 Example of an outfit illustration drawn by the same participant at low fertility (a) and high fertility (b). Source: Durante. K.M., Li, N.P. and Haselton, M.G. (2008) Changes in women’s choice of dress across the ovulatory cycle: Naturalistic and laboratory taskbased evidence. Personality and Social Psychology Bulletin, 34, 11, 1451–60.
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Cutting edge – Continued This perception is mirrored in women’s own behaviour. Women were asked to report to a laboratory on high or low fertility days (confirmed by a hormone test) and to pose for photographs and draw an outfit that they would prefer to wear that evening (Durante et al., 2008). Women were more likely to sketch sexier outfits during the high fertility period – they drew more revealing outfits, as the example in Figure 3.10 shows. The more sexually experienced the woman, the skimpier the outfit. Single women drew more revealing outfits than those who had partners but the more satisfied the women were with their partners, the more revealing the outfit they drew (suggesting that they were confident to express their sexuality in the context of a secure relationship).
Monogamy: shared, but not always equal, parental investment Around 3 per cent of the relationships in mammals are monogamous. Monogamy has evolved in those species whose environments have favoured the contributions of both parents to the survival and reproductive success of their offspring. In other words, under some conditions, two individuals sharing parental duties enjoy more reproductive success than does one individual who must do it all alone. Although both parents in monogamous species share offspring-rearing duties, each parent may not make an equal contribution towards that end. Like females in polygynous species, females in monogamous species generally have greater parental investment in the offspring, for many of the same reasons: the limited opportunity for mating relative to that for males, pregnancy and its accompanying risks, providing milk to the newborns, and the time and energy spent in caring for them. As a result, very few monogamous species, including our own, are exclusively monogamous. In fact, there is a strong tendency in most monogamous species towards patterns of reproductive behaviour and parental investment that resemble those of polygynous species. For example, in monogamous species, females tend to be more careful than males in selecting a mate, and males tend to be more sexually promiscuous than females (Badcock, 1991). In our own species, men tend to engage in premarital sexual intercourse more often than do females (Kinsey et al., 1948, 1953; Hunt, 1974), although this gap appears to be decreasing. Men also tend to have more premarital and extramarital sexual partners (Symons, 1979), although recent studies show that over 90 per cent of male and female undergraduate respondents want to settle down with one partner exclusively at some point (Pedersen et al., 2002).
Psychologists from the University of Tromsø, Norway, have also recorded the way in which women’s pupils reacted as they watched photographs of either their boyfriends or celebrities (Laeng and Falkenberg, 2007). Fourteen women participated during three menstrual periods – luteal, ovulatory and menstrual. An eye-tracking device measured pupil size. (Pupil diameter increases when people are sexually aroused.) Women during the fertile phase of their cycle showed larger pupil diameter when viewing photographs of their boyfriends, but this effect was found only on those who did not use oral contraceptives.
Reproductive success today may not be thought of in terms merely of the number of children we have (although among some religious subcultures this is still an important measure of success), but in terms of how well individuals raise healthy, happy and well-adjusted children. Although most people have the biological capacity to produce a large number of children, many do not have the psychological or financial wherewithal to do so. Some people fear that a large family will reduce the amount of money they can make and will therefore lower their quality of life. Others see a large family as an impediment to obtaining career goals and other life aspirations. And still others simply have no desire to have any children at all.
Monogamy and hormones Some scientists have hypothesised that monogamy may be attributable to chemicals called hormones, described in detail in the next chapter (Young et al., 1998). These are generated by a region in the brain which sends signals to organs of the body to react in a certain way. The proposed relationship between hormones and monogamy has been based on studies of a type of rodent, the vole. Researchers have found that two types of vole show very different patterns of mating: the prairie vole is largely monogamous, forming lasting partnerships; the montane vole, however, is promiscuous and not a particularly social species. The male montane vole is not parental and does not form a bond with its partner; the female montane vole abandons its offspring around two to three weeks after birth (Young et al., 1998). Two key hormones have been identified that could underpin these behaviours: oxytocin (OT) and vasopressin (AVP). In prairie voles, vaginal-cervical copulation leads to an increase in the release of OT. This release may promote intense mating in females but has little effect on
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males. Vasopressin, however, does affect male prairie voles. Administering this hormone in these male voles leads to a preference for an exclusive partner, aggression towards strangers and an increase in paternal care (Young et al., 1998). In the montane male vole, the effect of the hormones is not aggression but self-grooming. The receptor distribution for these hormones in the brain of the prairie vole is similar to that in other monogamous types of vole; conversely, the distribution of receptors in montane voles is similar to other promiscuous vole types. Levels of oxytocin have recently been associated with trustworthiness and trustworthy behaviour in humans (Zak et al., 2005). Together, these findings suggest that there may be some hormonal basis to the monogamy seen in certain species and that this hormonal basis arises from receptor distributions which, in turn, arise from the expression of a gene. The idea is controversial and provocative but interesting. It is unclear, with primates’ high degree of (largely) sophisticated social interaction, whether such endocrinal expressions could explain monogamy and promiscuity in humans.
Infidelity It has been estimated that between 20 and 50 per cent of people who are married will be unfaithful to each other at some point (Thompson, 1983; Wiederman, 1997), and men claim to want a greater number of sexual partners across a lifetime than do women. For various evolutionary reasons, evolutionary psychologists suggest that men and women respond differently to different types of infidelity. Heterosexual men, for example, are more likely to show jealousy in response to sexual infidelity (a partner having sex with another man), whereas heterosexual women are more likely to show jealousy in response to emotional infidelity (a partner having a very deep, loving, yet non-sexual, relationship with another woman). A study in which male and female undergraduates were asked whether they would forgive the two types if infidelity in their partner conformed to the expected pattern and found that men were less likely to forgive sexual than emotional infidelity whereas women showed the opposite pattern (Shackelford et al., 2002). Men were also more likely to terminate a relationship if their partner committed sexual infidelity. Harris (2002) examined men’s and women’s responses to infidelity by giving them a scenario to respond to. As in most other studies, participants were asked whether they would be more upset if they found out that their partner was trying different sexual positions with another or if their partner was falling in love with another. Some 196 participants, with a mean age of 37, were recruited via newspaper advertisements and flyers. Harris was also interested in whether responses would be similar in
homosexual and heterosexual men and women and so recruited roughly equal numbers of each. Participants were asked if they had been ‘cheated’ on, whether they focused on the emotional or sexual consequences of the cheating and whether the relationship ended as a result. As predicted by evolutionary psychology, heterosexual men were more likely to find sexual infidelity more upsetting than they would emotional infidelity when responding to the forced-choice question. The reverse pattern was found for women. When participants recalled actual examples of infidelity, however, no sex differences were found. Regardless of sexual orientation, both men and women were more likely to focus on a partner’s emotional than sexual infidelity as the source of distress. No relationship was found between participants’ responses to hypothetical and actual infidelity. Harris (2002) concludes:
If emotional jealousy was selected for because it helps women prevent loss of a mate’s resources, then how did men come by such a mechanism?. . . the farther one moves away from asking college students the forcedchoice question regarding hypothetical infidelity toward assessing real infidelity with adults, the less support one finds for the [evolutionary] hypothesis.
People who are married to disagreeable, undependable and emotionally unstable partners are less satisfied with their marriage (Shackelford and Buss, 2000). Low agreeableness, low emotional stability and low conscientiousness in women is associated with low marital satisfaction in men. Disagreeable, emotionally unstable men were also more likely to abuse their wives than their agreeable, emotionally stable counterparts. Furthermore, mate-guarding tactics such as threatening infidelity, threatening to punish infidelity and emotional manipulation (i.e. the factors which inflict costs on a relationship) were associated with lower marital satisfaction in the people at the receiving end of these tactics. What makes a mate poacher? When infidelity occurs, are there factors that can dispose a person to being unfaithful and to wanting to have a relationship with a person who already has a partner? One study found that 84 per cent of undergraduates reported that attempts had been made to poach them from their partners (Schmitt and Buss, 2001). Of those who were romantically linked (just over 55 per cent), 20 per cent of men and 28 per cent of women stated that their partners had been poached from someone else. In terms of personality, agreeable and conscientious people were least likely to be mate poachers, a finding that is found internationally (Schmitt, 2004). Those who did not regard relationships
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Cutting edge – Jealousy, infidelity and the brain Although romantic jealousy seems more common in men than women, the sexes may also differ in what they become jealous about. Men are more likely to be jealous, angry and upset about sexual infidelity whereas women are more likely to be upset by emotional infidelity (their partner engaging in a warm and fulfilling friendship with another woman). These differences might have a neural basis (Takahashi et al., 2006). Twenty-one men and women read the statements in Table 3.3 silently as brain activation was recorded. They read the statements again after scanning and were asked how they would feel if their boyfriend or girlfriend was the protagonist. Men and women did not differ significantly in terms of the types of infidelity they felt jealous about – both sexes became
equally jealous under both conditions (emotional or sexual infidelity). However, brain activation did differ by sex. Men showed greater activation in the amygdala during sexual jealousy and in the hypothalamus during emotional infidelity. These are structures involved in sexuality and reproduction, amongst other functions. Women showed greater activation in the posterior superior temporal sulcus, an area the authors suggest is implicated in ‘the detection of others’ intention or violation of social norms’. The data from this small group of healthy young adults suggest that subtle neural differences might underlie jealous responses to certain types of infidelity.
Table 3.3 Examples of the jealousy-arousing sentences used in Takahashi et al.’s study Neutral My girlfriend stayed in a twin-bed room in a hotel with her female friend My girlfriend wrote a new year’s card to her female friend My girlfriend spent a night in her female friend’s room My girlfriend meets her best female friend frequently My girlfriend had her coat taken off by her female friend My girlfriend telephones her parents on the weekend My girlfriend e-mailed her mother yesterday. Sexual infidelity My girlfriend stayed in a double-bed room in a hotel with her ex-boyfriend My girlfriend took a bath with another man My girlfriend had her underwear taken off by another man My girlfriend spent a night in her ex-boyfriend’s room My girlfriend kissed another man deeply My girlfriend passionately embraced another man My girlfriend took an overnight trip with another man My girlfriend was naked with her ex-boyfriend in his bed. Emotional infidelity My girlfriend wrote a love letter to another man My girlfriend had dinner with another man on my birthday My girlfriend supplied another man with all the money she had saved My girlfriend telephones her ex-boyfriend every day My girlfriend always talks with delight about her ex-boyfriend in front of me My girlfriend emails to her ex-boyfriend every night My girlfriend gave gorgeous birthday presents to her ex-boyfriend My girlfriend meets another man more frequently than she does me
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as exclusive and described themselves as having erotophilic tendencies – a constant desire to satisfy sexual needs – were more likely to poach. These individuals also scored high on sexual attractiveness: it appears that the poacher may have to be sexy, as well as adulterous. Extraverts were more likely than introverts to be recipients of poaching attempts. Those who rated themselves as sexually attractive, as not relationship exclusive and as emotionally investing (loving) were those who were most likely to be poached. Physical attractiveness was more important for men than it was for women. Women, conversely, were more likely to view resource acquisition as a benefit of poaching, especially in short-term relationships. Because men value physical attractiveness in women, women pay greater attention to using physical characteristics as cues to attraction. Women, on the other hand, placed greater value on resources. Men, consequently, emphasised cues that indicate that they are resource-laden (such as expensive clothes, cars, jewellery and so on). Women who thought they could make themselves more attractive by disparaging the partner of the person they wanted to poach were not as effective as enhancing physical attractiveness. As predicted, men were found to be more successful than women at poaching when they displayed resources. Men who showed displays of dominance were also more likely to be effective at poaching in the short term, but this factor was not rated very highly. Getting a mate drunk was an ineffective poaching cue in the long term but one with moderate success in the short term, especially when used by women. Men were more effective at using humour as a poaching cue than were women in the short and long term. Women employed a tactic that was significantly more effective when used by them than by men: boosting the partner’s ego. When the relationship of the person who was being poached was long-distance, not committed or about to end, poaching was effective; when the relationship involved marriage, great commitment, living together or just beginning, poaching was seen as ineffective. Although based on a sample of undergraduates, and assessing perceived effectiveness rather than actual effectiveness of poaching, this series of studies shows that poaching is a common phenomenon and that men and women use different cues with varying degrees of success to poach a mate from their existing partner.
Promiscuity Promiscuity – the tendency to engage in sexual activity with multiple partners (not necessarily at the same time) – has been associated with specific personality types. Sensation-seekers, for example, have more partners than
low sensation-seekers; and the unconscientious, extravert, the less agreeable and more antagonistic similarly report having more sexual partners than the conscientious, the less extravert and the more agreeable/less antagonistic. A new study has associated two other factors with this behaviour (Markey and Markey, 2007). In a study of 105 young men and 105 young women, people who were dominant had significantly more sexual partners than did those who were less so. Curiously, people who were personally warm were also more likely to have had more sexual partners than the less warm. ‘This indiscriminate behaviour [promiscuity]’, the authors conclude, ‘may not always be ill-intentioned but, in some cases, may be an expression of warmth.’ Commenting on the findings regarding dominance, the authors suggest that ‘selective participation in sexual behaviours may be a reflection of an individual’s submissiveness, not their “moral piety”’. A related study examined whether men who engaged in unrestricted sexual activity – engaging in transient sexual relations – perceived women’s attractiveness differently from men who were more restricted (Swami et al., 2008). Men self-described as restricted or unrestricted rated the attractiveness of drawings of women who differed according to Body Mass Index and waist-to-hip ratio. The men, regardless of type, used BMI rather than WHR as the basis of their judgement but unrestricted men found women with lower BMI to be more attractive and healthy than did restricted men. The unrestricted men also preferred women with a low WHR.
Polyandry: high male and low female parental investment Polyandry is a rare reproductive strategy among humans and non-existent in other mammals. It is more prevalent among species that lay eggs. Once the eggs are laid, then either the male or the female may take care of them, although in many instances the male makes the greater investment of time and effort. An example of polyandry in humans is found among some of the people who live in remote Himalayan villages. These people are extremely poor and live in a harsh environment, which makes their primary livelihood, farming, difficult. In order to prevent the dissolution of family farms through marriage, families that have more than one son limit the number of marriages to only one per generation – several brothers may share the same wife. A female tends to marry more than one man (most often brothers) to guarantee that she will be adequately supported. In other words, the male’s primary investment – the farm, which is the source of food and some income for the family – is guarded jealously through polyandry.
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Infidelity – An international perspective
Polygynandry: group parental investment Many primates, such as chimpanzees, live in colonies in which few or no barriers are placed on which female mates with which male. In other words, the colonies are promiscuous – during periods of mating, intercourse is frequent and indiscriminate. What is the advantage of such a reproductive strategy? The primary advantage seems to be the cooperation of males and females in the colony with respect to rearing offspring. Because the males in the colony are not sure which
70 65 Long-term poaching attempted (%)
While some of the psychological characteristics of mate poachers and mate poaching are well documented, the extent of the behaviour cross-culturally is less well documented. Evolutionary psychologists argue that the nature and degree of mate poaching/poachers should be similar across cultures but with some provisos. Studies show that men are more likely than women to engage in short-term mate poaching and so we might expect this finding across cultures. However, we might also expect cultures which observe traditional sex roles to show a bigger difference between men and women than cultures that are more liberal and egalitarian. In demanding environments (those that afford fewest resources), there may be less of an opportunity or a desire for mate poaching because the difficulties involved in raising a family require commitment from both partners. These predictions were tested by Schmitt and colleagues (Schmitt et al., 2004) in a study of 16,954 individuals from 53 nations, divided into 10 world regions (North America, South America, western Europe, eastern Europe, southern Europe, the Middle East, Africa, Oceania, South/Southeast Asia, and East Asia). Mate poaching overall was very common – 70 per cent reported that they had been the object of a poaching attempt. Eighty per cent of poaching attempts were apparently successful with 10 per cent of such attempts leading to a long-term relationship. Mate poaching was most common in southern Europe, South America and western Europe and was least common in Africa, South/Southeast Asia and East Asia, a finding that is consistent with the prediction regarding demanding environments. The number of attempts at mate poaching by members of various cultures can be seen in Figure 3.11. Also consistent with the study’s predictions, men were more vigorous mate poachers than were women, with 60 per cent of men reporting that they had attempted to mate poach and 40 per cent of women reporting so. In cultures where men and women were regarded as equals, this sex difference was smaller. In keeping with previous studies, the personality measures showed that poachers were extraverted, disagreeable, uncon-
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North America
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Eastern Europe Southern Europe
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Africa
Middle East Oceania
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30 25 20 90
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Operational sex ratio
Figure 3.11 The degree of mate-poaching across nations and cultures. Euopeans and Americans seem especially keen on it. Source: D.P. Schmitt, Patterns and universals of mate poaching across 53 nations: The effects of sex, culture and personality on romantically attracting another person’s partner, Journal of Personality and Social Psychology, 2004, 86 (4), 560–84, Figure 2.
scientious, slightly narcissistic and (no surprise here) unfaithful. The poached were likely to be extraverted, open, attractive and disagreeable. Both groups were likely to be highly sexual. Of course, the majority of the study’s participants were young undergraduates and the authors note that mate poaching may be more common in this younger group than in an older sample. They also note that studying young married couples would be informative because men are reported to be highly jealous if an attempt is made to woo their wives. These men also appear to be more vigilant in observing such attempts. It would also be useful to measure the degree of satisfaction with a poacher’s current relationship and whether this, rather than some personality profile, is the key predictor of poaching.
offspring belong to them, it is in their best interest to help rear and protect all the offspring and defend their mothers. The unity in the colony and the lack of aggression among the males contributes directly to the general welfare of all colony members. Females and males have access to many mates, and the offspring are well cared for. However, a form of monogamy called a consortship is sometimes observed in polygynandrous species. For instance, a particular male chimpanzee may ward off other male suitors from a particular female, resulting in an exclusive sexual union. If successful, he is guaranteed
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the certainty of which offspring are his, albeit at some cost. There is a chance that he could be seriously injured in protecting his mate from other males, and therefore he becomes less useful as a parental investor in his offspring or those of the colony.
Incestuous relationships: a universal taboo All reproductive strategies seem to have one element in common: avoidance of incest. Incest is the mating of kin who share many of the same genes. Avoidance of incest appears to have evolved for a very good reason: closely related relatives are likely to share the same recessive genes that cause genetic disorders. Thus, animals that avoid incestuous matings have an evolutionary advantage over those that do not; they produce healthier offspring who themselves are more likely to live to sexual maturity and produce offspring of their own. All human cultures have taboos against incest. A taboo is a societal rule prohibiting the members of a given culture from engaging in specific behaviours – in this case, mating with a genetically related individual. Taboos are products of cultural evolution and are socially transmitted through language from one generation to the next. Incest taboos are probably of secondary importance, serving to reinforce the aversion we have towards incest or mating with non-relatives with whom we were raised. For example, in one study (Shepherd, 1983), the elders actually encouraged the children of the kibbutz to marry so that the children would not end up living far from home. Despite the absence of a taboo and the encouragement of the elders, none of the children married each other.
Altruism and kin selection A particularly interesting and important social behaviour in terms of evolution is altruism, the unselfish concern of one individual for the welfare of another. Examples of altruistic behaviour abound and its most extreme form is when one person risks their life to save the life of another. Examples of altruism are also common throughout the animal kingdom. The honey bee, for example, sacrifices its life on behalf of its hivemates by stinging an intruder. Here, the altruist’s chances of survival and reproductive success are lowered while that of the other individuals are raised. Sociobiologists seek out ultimate causes, especially the consequences of natural selection, to explain altruism. They assert that natural selection has favoured the evolution of organisms that show altruistic tendencies. However, there is an important problem here. On the surface, altruism poses an enigma to evolutionary theory. Recall that according to natural selection only phenotypes that enhance one’s reproductive success are
favoured. How could altruistic behaviour have evolved given that, by definition, it is less adaptive than selfish or competitive behaviour? The geneticist William D. Hamilton (1964, 1970) suggested an answer to this question in a series of mathematical papers. Hamilton’s ideas stemmed from examining natural selection from the perspective of the gene instead of from the perspective of the whole, living organism. He argued that natural selection does not favour mere reproductive success but rather inclusive fitness, or the reproductive success of those individuals who share many of the same genes. Altruistic acts are generally aimed at close relatives such as parents, siblings, grandparents and grandchildren. The closer the family relation is, the more likely the genetic similarity among the individuals involved. Such biological favouritism towards relatives is called kin selection (Maynard Smith, 1964). The message here is clear: under the proper circumstances, individuals behave altruistically towards others with whom they share a genetic history, with the willingness to do so decreasing as the relative becomes more distant. In this view, altruism is not necessarily a conscious act but rather an act driven by a biological prompt that has been favoured by natural selection. Natural selection would favour this kind of altruism simply because organisms who share genes also help each other to survive. Parenting is a special case of kin selection and an important contributor to one’s survival and reproductive success. In the short run, parents’ altruistic actions promote the continued survival of their offspring. In the long run, these actions increase the likelihood that the offspring, too, will become parents and that their genes will survive in successive generations. Such cycles continue according to biological schedule, generation after generation. In the words of sociobiologist, David Barash (1982, pp. 69–70):
It is obvious why genes for parenting have been selected: all living things are the offspring of parents who themselves were [the offspring of ] parents! It is a guaranteed, unbroken line stretching back into time. [Genes] that inclined their bearers to be less successful parents left fewer copies of themselves than did those [genes] that were more successful.
What is at stake is not the survival of individual organisms but the survival of the genes carried by those organisms. Genes allow organisms to maximise their inclusive fitness through altruistic behaviour directed at other organisms sharing the same genes (Dawkins, 1986). Inclusive fitness refers to the idea that reproduction and natural selection occurs because a species’ success is
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measured through the production of offspring. You carry copies of genes that have been in your family line for thousands of years. When the opportunity presents itself, you will most likely carry on the tradition – reproducing and thus projecting your biological endowment into yet another generation. But you did not reach sexual maturity on your own; the concern for your welfare by your parents, brothers, sisters, grandparents and perhaps an aunt or uncle has contributed to your chances of being reproductively successful. Genes not projected into the next generation simply disappear. Another variable may mediate altruism, however: emotional closeness. Emotional closeness is defined as having a sense of concern and caring for another and enjoying a comforting, emotional relationship with them. One study asked participants to rate how willing they would be to behave altruistically towards members of their family when the family member could live or die, and when helping would be at a cost to the participant (Korchmaros and Kenny, 2001). Participants also indicated how emotionally close they were to these family members. People were more likely to help family members with whom they shared a close relationship, regardless of the genetic closeness of the relationship, than with those with whom they shared a less close relationship. The findings suggest that emotional closeness may be a mediating cause of altruistic behaviour. Evidence from step-relations’ behaviour supports the idea of inclusive fitness. It has been reported, for example, that a disproportionate number of children in stepfamilies suffer physical harm, especially assault (Daly and Wilson, 1988). Child battering is more common in stepfamilies, as is the incidence of child abuse (Daly and Wilson, 1996). This evidence, the sociobiologists argue, supports the notion than non-genetic relatives are not disposed to invest resources in offspring that are genetically unrelated. There is also evidence to suggest that cohabitation is a greater risk factor for spousal murder than is marriage. Canadian research published at the beginning of the 1990s suggested that women in cohabiting relationships were more likely than married women to be murdered by their partner (Wilson et al., 1993, 1995). Data from specific US cities show the same pattern (e.g. Wilbanks, 1984). According to the Wilson et al. studies, women in their early twenties were at greater risk of homicide if they were married; for cohabiting women, women in their mid-thirties to forties were at greatest risk. A national study of over 400,000 US homicides committed between 1976 and 1994 found that women in cohabiting relationships were nine times more likely than married women to be murdered by their partner (Shackelford, 2001). The risk for married women decreased as they became older. Middle-aged women, however, were at greatest risk if they were in a cohabiting relationship.
Young men were more likely to murder their wives whereas middle-aged men were more likely to murder their cohabiting partners. One explanation for these findings is that men may tend to feel significantly and abnormally proprietorial about their partners, especially about their partner’s sexuality. A man in a cohabiting relationship is more insecure than is a married man because the possibility of either partner leaving the relationship is more likely and is easier to do. The cohabiting man may, therefore, go to more extreme lengths to prevent his partner from leaving him than would a married man because cohabiting relationships are more likely to break than are marriages. There is some evidence in support of this interpretation. Daly and Wilson (1988), for example, cite their partner data showing that men who kill their partners are more likely to do so because they suspect that their partner has been unfaithful or may be about to terminate their relationship.
Reciprocal altruism Kin selection explains altruism towards relatives, but what about altruism directed towards non-relatives? According to Trivers (1971), this kind of altruism, called reciprocal altruism, exists because humans (and other organisms) can function more effectively if they work together. Human groups are hierarchical and cooperative (Buss, 1995), whether at the level of the family, canoe club or workplace. There is also evidence that kindness, dependability, emotional stability and intelligence (all traits one would associate with altruism) are the most valued personality characteristics in potential mates (Buss, 1995). Cooperation between groups is a fundamental survival strategy (Brewer and Caporael, 1990), and is seen in many higher primates (Byrne, 1995). For example, in order to win a mate from a dominant male savannah baboon, a male will engage the help of another baboon who will distract the dominant male and enter into a fight with him. This leaves the other, non-dominant male free to mate with the female. The altruism is reciprocal because the favour will be reciprocated by the successfully paired male in the future (Haufstater, cited in Byrne, 1995). Another primate example where reciprocal altruism can be seen is in food sharing and also in a task called the prisoner’s dilemma.
The prisoner’s dilemma An illustration of the way in which reciprocal altruism can work is provided by the ‘prisoner’s dilemma’ (Axelrod and Hamilton, 1981). The prisoner’s dilemma is a scenario in which individuals are allowed to cooperate or not cooperate. Two suspects are imprisoned separately and are asked to consider being silent (to cooperate) or sing (to defect).
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If both prisoners cooperate then they both get lighter sentences; but if one sings then that prisoner gets off still more lightly. If the game is played once, defection is the best strategy; however, if the game is played repeatedly then staying silent might be the best option because the other player can return the favour or punish the defection. Nowak and Sigmund (1998) have suggested that cooperation can still be established even if there is no chance for the cooperation to be reciprocated. The reason for this is that an individual seen to be cooperative or having a reputation for being cooperative will be more likely to experience reciprocal behaviour from others in future. In short, helping will be rewarded by someone who acknowledges your good reputation. The prisoner’s dilemma may not be the most effective test of cooperation because it allows only cooperation or defection. In real life, however, cooperation is not an allor-nothing behaviour. Some individuals may invest slightly less in cooperation, some slightly more, but they may all cooperate in some form. Imagine two individuals giving to charity: one gives £10, the other gives £100. Both are cooperating (being altruistic), but one is more altruistic than the other (one may be able to afford the £100 but the other is making a financial sacrifice by donating £10). Because of this variation in altruism, Roberts and Sheratt (1998) have suggested a ‘raise the stakes’ model of altruistic behaviour. This model argues that individuals would offer a small amount at the first meeting and if this amount is reciprocated, then more will be offered at the next opportunity. This model suggests that behaviour cannot be effectively exploited and so cooperation would be enhanced.
Sociobiology and evolutionary psychology as an explanation for human behaviour? So far in this chapter you have seen that sociobiologists attempt to explain social behaviour by reference to natural selection and genetic inheritance. Evolutionary psychologists ‘develop hypotheses about the psychological mechanisms that have evolved in humans to solve the particular adaptive problems that humans have faced under ancestral conditions’ (Buss, 1995, p. 4). Sociobiology has been at the centre of a fierce scientific controversy ever since E.O. Wilson published Sociobiology: The new synthesis in 1975, the official birth date of this discipline. Although Wilson’s work, which is based chiefly on studies of non-human animal behaviour, has generated an enormous outpouring of scientific research, it has also roused a number of serious charges (Montagu, 1980). Wilson’s On Human Nature (1978), which extended sociobiological theory to human affairs, ignited even more
criticism. Most of the criticism focuses on the extension of the theory to human behaviour. Two issues which have caused greatest controversy are inclusive fitness and the mechanisms of adaptation. Recall that inclusive fitness theory argues that reproduction and natural selection occur because species’ survival success is measured through the production of offspring. Those characteristics which help promote the transmission of genes (either directly or indirectly) will be naturally selected, akin to Dawkins’s sieve mentioned at the beginning of the chapter. Sociobiologists see humans as ‘fitness maximisers’, or ‘fitness strivers’ (Alexander, 1979), constantly applying the mechanisms for maximising inclusive fitness. The evolutionary psychologists, however, call this the ‘sociobiological fallacy’ (Buss, 1991, 1995) because it confuses the theory of origins of mechanisms with the theory of the nature of mechanisms. As Buss argues, if humans were ‘fitness maximising blobs’, why are men not queuing up at sperm banks to donate their sperm? Why do some couples forgo reproduction? We have developed a preference for fatty foods but this is known to be detrimental to us. If we know this food is unhealthy, why do we eat it? More to the point, we can look at individuals or their behaviour and easily find maximising fitness reasons for this behaviour. The inclusive fitness theory, therefore, cannot account for natural selection and, because of its breadth (one can interpret almost any behaviour in terms of maximising fitness), is virtually limitless in its application. Instead of seeing humans as fitness maximisers, evolutionary psychologists see humans as ‘adaptation executors’ or ‘mechanism activators’ (Tooby and Cosmides, 1990). That is, humans apply evolved solutions to adaptive problems (Buss, 1995). These solutions are domain-specific. That is, the types of solution one would need to reach to select a mate are different from those one needs to obtain food or to parent children. Adaptive problems are large, complex and varied; the success of individuals in solving these problems depends on sex, species, age, context and individual circumstances (Buss et al., 1998). Sociobiology, however, seems to ignore this psychological level of interpretation and goes from evolution straight to patterns of social organisation. The most intense criticism of sociobiology is political, not scientific. Opponents argue that sociobiology sanctions the superiority of one group over another, be it a race, a gender, or a political organisation. After all, they argue, if one group of individuals is genetically superior to another, then there are ‘natural’ grounds for justifying the ‘survival of the fittest’ and one group’s unethical and immoral domination of another. An example is Hitler’s quest for world domination in the name of Aryan superiority. Sociobiologists flatly deny such allegations and argue that it is the critics and not they who have confused the term
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‘natural’ with the terms ‘good’ and ‘superior’. Are political objections to sociobiology scientifically acceptable ones? Do you think that psychologists should be concerned with political objections to their findings or theories? Given the broad-sweep nature of sociobiological theory, it is not surprising that the theory fails to account
adequately for natural selection. Although kin selection and familial altruism could be interpreted as supporting the inclusive fitness theory, it is true that one could explain away a lot of behaviour by describing it as maximising fitness.
Chapter review Natural selection and evolution • Understanding behaviour requires that psychologists learn
•
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more about both proximate causes of behaviour – how animals adapt to environmental changes through learning – and ultimate causes of behaviour – historical events and conditions in the evolution of a species that have shaped its behaviour. Darwin’s voyage on the Beagle and his subsequent thinking and research in artificial selection led him to develop the idea of biological evolution, which explains how genetic and physical changes occur in groups of animals over time. The primary element of biological evolution is natural selection: the tendency of some members of a species to produce more offspring than other members do. Members of a species vary genetically; some possess specific traits to a greater or lesser extent than other individuals do. If any of these traits gives an animal a competitive advantage over other members of the species then that animal is also more likely to have greater reproductive success. Its offspring will then carry its genes into future generations. Two important adaptations during the course of human evolution are bipedalism – the ability to walk upright – and encephalisation – an increase in brain size. The combination of these two factors allowed early humans to explore and settle new environments and led to advances in tool making, hunting, food gathering and self-defence. Encephalisation appears to have been associated with language development and cultural evolution. The study of the evolution of our species suggests the nature of the circumstances under which adaptive behaviour first emerged and those circumstances that have been important for its continued expression to the present time.
Heredity and genetics • The instructions for the synthesis of protein molecules, which oversee the development of the body and all of its processes, are contained in genes. Genes are found on chromosomes, which consist of DNA and are found in every cell. • Humans inherit 23 individual chromosomes, each of which contains thousands of genes, from each parent. This means that our genetic blueprint represents a recombination of the genetic instructions that our parents inherited from their parents.
• Such recombination makes for tremendous genetic diversity. Genetically diverse species have a better chance of adapting to a changing environment than do genetically non-diverse species because some members of the species may have genes that enable them to survive in a new environment. • The expression of a gene depends on several factors, including its interaction with other genes (polygenic traits), the sex of the individual carrying the particular gene, and the environmental conditions under which that individual lives. Changes in genetic material caused by mutations or chromosomal aberrations lead to changes in the expression of a particular gene. For example, haemophilia, an increased tendency to bleed from even minor injuries, is the result of a mutation, and Down syndrome, which involves impaired mental, physical and psychomotor development, is the result of a chromosomal aberration. • Behaviour genetics is the study of how genes influence behaviour. Psychologists and other scientists use artificial selection studies of animals, twin studies, and adoption studies to investigate the possible relationship between genes and behaviour in humans. • Recent studies suggest that the attitudes and personalities of identical twins are more closely related than are those of fraternal twins.
Sociobiology • The discovery of the biological basis for social behaviour is the primary goal of sociobiology. Sociobiologists have been especially interested in studying social behaviour related to reproduction and the rearing of offspring. • Evolutionary psychology is a relatively new sub-field of psychology (and sociobiology) that is devoted to the study of how evolution and genetic variables influence adaptive behaviour. • Different reproductive strategies are believed to have evolved because of sex differences in the resources that parents invest in procreative and child-rearing activities. These resources include the time, physical efforts and risks to life involved in procreation and in the feeding, nurturing and protection of offspring. • A low waist-to-hip ratio appears to be preferred by Western heterosexual men; a waist-to-chest ratio that emphasises narrow hips and broad shoulders is preferred by Western heterosexual women. In some cultures, however, there is a
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preference for heavier, larger women. One reason for this is that these cultures may not have been exposed to the Western ideals of physical beauty, those which emphasise the curvaceousness of women. • Recent research suggests that facial attractiveness may be a more important determinant of mate selection than is waist-tohip ratio. • Polygynous and monogamous strategies tend to require greater female investment, polyandrous strategies tend to require greater male investment, and polygynandrous strategies tend to require investment on the part of members of a large group, such as a colony of chimpanzees. Despite these differences, all reproductive strategies entail avoidance of incest, either through migration or the recognition of closely related genetic kin or those individuals with whom one was raised. All human cultures have taboos about incest. • Altruism is difficult to explain by appealing to natural selection. Altruistic behaviour generally involves one organism risking its life for others with whom it shares some genes (kin selection)
or who are likely subsequently to be in a position to return the favour (reciprocal altruism). • Inclusive fitness theory argues that reproduction and natural selection occur because species’ survival success is measured through the production of offspring. Those characteristics which help promote the transmission of genes (either directly or indirectly) will be naturally selected. • Sociobiology has been criticised on the grounds that natural selection is no longer a factor in human evolution, that research on animal social behaviour is not relevant to understanding human social behaviour, that environmental factors play a greater role in shaping human behaviour than genetic factors, and that sociobiology is simply a way to justify the superiority of one group over another. Sociobiologists reply that natural selection has shaped and continues to shape the evolution of culture, that findings from animal research can be generalised to humans, that genes and environment interact to determine behaviour, and, finally, that sociobiology is an attempt to understand human behaviour, not to justify it.
Suggestions for further reading Evolution: Popular accounts Brown, A. (2000) The Darwin Wars. London: Simon & Schuster. Darwin, C. (1859) The Origin of Species by Means of Natural Selection. London: Murray. Dawkins, R. (1986) The Blind Watchmaker. London: Penguin. Dawkins, R. (1989) The Selfish Gene. London: Penguin. Dawkins, R. (2003) A Devil’s Chaplain. London: Weidenfeld & Nicolson. Dawkins, R. (2009). The Greatest Show on Earth: The Evidence for Evolution. Bantam Press Dennett, D.C. (1995) Darwin’s Dangerous Idea. London: Penguin. Scientific American Mind, special edition on ‘Becoming Human: evolution and the rise of intelligence’, 2006, 16, 2. Some good introductions to evolutionary theory.
Evolution and the brain Duchaine, B., Cosmides, L. and Tooby, J. (2001) Evolutionary psychology and the brain. Current Opinion in Neurobiology, 11, 225–30. Roth, G. and Dicke, U. (2005) Evolution of the brain and intelligence. Trends in Cognitive Sciences, 9, 5, 250–57. Both items provide a good grounding in the evolution of the brain.
Behavioural genetics Eley, T.C. and Craig, I.W. (2005) Introductory guide to the language of molecular genetics. Journal of Child Psychology and Psychiatry, 46, 10, 1039–41. Plomin, R. (2008) Behavioural Genetics. London: Palgrave. Plomin, R. (2005) Finding genes in child psychology and
psychiatry: When are we going to be there? Journal of Child Psychology and Psychiatry, 46, 10, 1030–38. Plomin, R. and Colledge, E. (2001) Genetics and psychology: Beyond heritability. European Psychologist, 6, 4, 229–40. Scerif, G. and Karmiloff-Smith, A. (2005) The dawn of cognitive genetics? Critical developmental caveats. Trends in Cognitive Sciences, 9, 3, 126–36. These items give a useful introduction to behavioural genetics (and objections to behavioural genetics).
Evolutionary psychology and sociobiology Buss, D.M. (2008) Evolutionary psychology: The new science of mind (3rd edn). Boston: Allyn & Bacon. Matsuzawa, T. (2008) Primate origins of human cognition and behaviour. New York: Springer. Pigliucci, M. (2006) Is evolutionary psychology a pseudoscience? Skeptical Inquirer, 30, 2, 23–4. Rose, H. and Rose, S. (2000) Alas, Poor Darwin. London: Jonathan Cape. Wilson, E.O. (1975) Sociobiology: The new synthesis. Cambridge, MA: Harvard University Press. Workman, L. and Reader, W. (2004) Evolutionary psychology. Cambridge: Cambridge University Press. These selected readings are a good introduction to sociobiology and evolutionary psychology. Donald Buss is a highly active researcher and thinker in evolutionary psychology; his book is a very good review of the limits and frontiers of this controversial sub-area. The Workman and Reader book is similar. Wilson’s book is a classic in this area. The Roses’ edited book is a collection of tendentious essays on evolutionary psychology, with Pigliucci also providing a critical perspective.
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Comparative evolution Byrne, R. (1995) The Thinking Ape: Evolutionary origins of intelligence. Oxford: Oxford University Press. Richard Byrne’s excellent little book is a provocative and detailed account of the evolution of intelligence in primates from the perspective of evolutionary psychology.
Journals to consult American Psychologist
Journal of Evolutionary Psychology
Behavior Genetics
Journal of Personality and Social Psychology
Child Development
Nature
Developmental Psychology
Personality and Individual Differences
Ethology and Sociobiology
Science
Human Nature, Motivation and Emotion
Website addresses http://www.darinday.org/englishL/home/index.html A website celebrating the 200th anniversary of Darwin’s birth.
http://www.arts.uwaterloo.ca/~acheyne/pce.html You’ll find more links to evolution sites here.
http://darwin-online.org.uk/ An online collection of Darwin’s manuscripts and other materials.
http://www.uni-saarland.de/fak5/ronald/ A link to Ronald Henss’s website which allows you to participate in online experiments on physical attractiveness.
http://www.pbs.org/wgbh/evolution/ A general, non-specialist introduction to evolution. http://cogweb.ucla.edu/EP/ A large collection of links to evolutionary psychology, adaptation, paleoanthropology and evolution topics.
http://www.envoyage.com/ A site dedicated to evolutionary psychology. http://www.georgetown.edu/research/gucdc/hugem/Wfacts.htm A collection of genetics fact sheets from the University of Georgetown.
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Found: the brain’s centre of wisdom Jonathan Leake, Science Editor
Scientists have identified the seat of human wisdom by pinpointing parts of the brain that guide us when we face difficult moral dilemmas. Sophisticated brain scanning techniques have found that humans respond by activating areas associated with the primitive emotions of sex, fear and anger as well as our capability for abstract thought. The findings, to be published in the Archives of General Psychiatry, represent a significant incursion into territory once regarded as the domain of religion and philosophy. Source: The Sunday Times, 5 April 2009
Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activities on: Brain structure and function • Brain damage • The autonomic nervous system • The endocrine system • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 4
• Describe the major parts of the nervous system and its principal components.
• Describe and understand the most important functions of these components.
• Describe the parts of a nerve cell and how it functions. • Understand how nerve cells communicate with each other.
• Describe the various techniques used in neuroscience and psychobiology to study behaviour, from lesioning to heart rate recording to neuroimaging.
• Describe the lobes of the brain and their function. • Be aware of the effects of drugs on behaviour and how they act on the brain to produce these behaviours.
• Be able to understand some of the psychobiological causes and correlates of behaviour.
QUESTIONS TO THINK ABOUT
• Are two human brains exactly alike? • Do psychological functions such as language, memory or visual perception reside in specific parts of the brain?
• Do different sides of the brain undertake different functions? If they do, what purpose would this serve?
• What do you think scientists mean by ‘nature v. nurture’ explanations? Is this concept a sensible one?
• How can we measure the brain and body’s responses to external and internal stimuli?
• Is any chemical that has an effect on our body and brain ‘a drug’?
• Why do certain drugs have different effects on our behaviour?
• If a person needs a drug to function efficiently, in what way could he or she be said to ‘abuse’ it?
CHAPTER 4
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The brain looks like a lump of porridge and has the consistency of blancmange. This organ, weighing an average 1400 g in an adult human, is the most important part of the body (it was not always so – Aristotle, for example, believed that the heart was more important to behaviour). It contains an estimated 10 to 100 billion nerve cells and about as many supporting cells, which take care of important support and ‘housekeeping’ functions. The brain
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The nervous system: the brain and its components
The central nervous system
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yp The brain has two primary functions: the sych control of behaviour and the regulation of the body’s physiological processes. The brain cannot act alone – it needs to receive information from the body’s sense receptors and it must be connected with the muscles and glands of the body if it is to affect behaviour and physiological processes. The spinal cord is a long, thin collection of nerve cells attached to the base of the brain and running the length of the spinal column (see Figure 4.1). It contains circuits of nerve cells that control some simple reflexes, such as automatically pulling away from a painfully hot object. The central nervous system communicates with the rest of the body through the nerves – bundles of fibres that transmit information in and out of the central nervous system. The nerves, which are attached to the spinal cord and to the base of the brain, make up the peripheral nervous system. The human brain has three major parts: the brain stem, the cerebellum and the cerebral hemispheres. Figure 4.2 shows photographs of the side (a), top (b), cross-section (c) and bottom/underneath (d) of the human cerebral hemispheres. The lower part of the cerebellum and brain stem projects beneath the cerebral hemisphere (see the bottom left of Figure 4.2 (a)); the upper part is normally hidden. If the human brain is removed from the skull, it looks as if it has a handle or stem. The brain stem is one of the most primitive regions of the brain, and its functions are correspondingly basic – primarily control of physiological functions and automatic behaviours such as swallowing and breathing. The brains of some animals, such as amphibians, consist primarily of a brain stem and a simple cerebellum. m
In Chapter 1 you saw that psychology is a discipline with many subdivisions. Sometimes these subdivisions are further subdivided into more specific areas of study. Psychologists who study the role of physiology in behaviour, for example, may be interested only in specific behaviours, organisms and techniques. Consequently, psychologists who specialise in researching the role of the brain and body in behaviour are known by different names. Psychobiology is the study of the role of physiology and anatomy in the regulation and execution of behaviour – these topics can range from the role of hormones in sexual reproduction, the effect of glucose deprivation on hunger, the relationship between hormone secretion and stress, the effect of relaxing music on heart rate, or the activation of the brain while a person is engaged in a particular task. Neuroscientists study similar processes but limit themselves to studying certain parts of the body – the brain and spinal cord. Together these parts are known as the central nervous system (CNS), so called because not only do they occupy the central position of the body but they are also the most important part of the nervous system for maintaining and producing behaviour. Neuroscientists study the CNS of any organism that possesses one. Neuropsychologists, as you saw in Chapter 1, study the relationship between the brain and its function. A goal of neuropsychology is localisation of function – the idea that parts of the brain perform specific functions. Although much of the research in neuropsychology derives from the effects of brain damage on behaviour, neuropsychologists also study psychological function in healthy individuals by using modern neuroimaging techniques (described later on). Psychophysiologists study physiological processes such as heart rate, hormone secretion, brain electrical activity and skin conductance and the conditions in which changes to these processes arise.
contains many different types of nerve cell which differ in shape, size and the kinds of chemicals they produce. Although nerve cells of the brain are organised in modules – clusters of nerve cells that communicate with each other – individual modules do not stand alone. They are connected to other neural circuits, receiving information from some of them, processing this information and sending the results on to other modules. In his famous book The Modularity of Mind, the philosopher Jerry Fodor (Fodor, 1983) argues that particular modules have particular functions – just as the transistors, resistors and capacitors in a computer chip do – and are relatively independent of each other. Although this idea – modularity – is still controversial, the evidence broadly supports some degree of modularity in the brain. The aim of psychobiology and neuroscience is to understand how individual nerve cells work, how they connect with each other to form modules, and just what these modules do.
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Layers of meninges
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and thinking, too. The cerebellum in cross-section is on the bottom right of Figure 4.2 (c). Because the central nervous system is vital to an organism’s survival, it is exceptionally well protected. The brain is encased by the skull, and the spinal cord runs through the middle of a column of hollow bones known as vertebrae. Both the brain and the spinal cord are enclosed by a three-layered set of membranes called the meninges (meninges is the plural of meninx, the Greek word for ‘membrane’; meningitis is an inflammation of the meninges). The brain and spinal cord do not come into direct contact with the bones of the skull and vertebrae. Instead, they float in a clear liquid called cerebrospinal fluid (CSF). This liquid fills the space between two of the meninges, thus providing a liquid cushion surrounding the brain and spinal cord and protecting them from being bruised by the bones that encase them. The surface of the cerebral hemispheres is covered by the cerebral cortex (the word cortex means ‘bark’ or ‘rind’). The cerebral cortex consists of a thin layer of tissue approximately 3 mm thick. It is often referred to as grey matter because of its appearance. It contains billions of nerve cells and is the structure where perceptions take place, memories are stored and plans are formulated and executed. The nerve cells in the cerebral cortex are connected to other parts of the brain by a layer of nerve fibres called the white matter because of the shiny white appearance of the substance that coats and insulates them. Figure 4.3 shows a slice of the brain. As you can see, the grey matter and white matter are distinctly different. The human cerebral cortex is wrinkled in appearance; it is full of bulges separated by grooves. The bulges are called gyri (singular ‘gyrus’), and the large grooves are called fissures. Fissures and gyri expand the amount of surface area of the cortex and greatly increase the number of nerve cells it can contain. Animals with the largest and most complex brains, including humans and the higher primates, have the most wrinkled brains and, thus, the largest cerebral cortices.
The peripheral nervous system
Figure 4.1 The central nervous system (brain and spinal cord) and the peripheral nervous system (cranial nerves and spinal nerves).
The two cerebral hemispheres constitute the largest, and most recently developed, part of the human brain. The cerebellum, attached to the back of the brain stem, looks like a miniature version of the cerebral hemispheres. Its primary function is to control and coordinate movements, although recent research has highlighted its role in language
The peripheral nervous system consists of the nerves that connect the central nervous system with sense organs, muscles and glands. Nerves carry both incoming and outgoing information. The sense organs detect changes in the environment and send signals through the nerves to the CNS. The brain sends signals through the nerves to the muscles (causing behaviour) and the glands (producing adjustments in internal physiological processes). Nerves are bundles of many thousands of individual fibres, all wrapped in a tough, protective membrane. Nerve fibres transmit messages through the nerve, from a sense organ to the brain or from the brain to a muscle or gland.
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(a)
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Figure 4.2 The external features of the brain from four angles: (a) the side (sagittal), (b) top, (c) cross-section (lateral) (d) bottom/underneath. Source: Professor Peter Cull/Science Photo Library Ltd
Top
White matter
Sulcus Synapse Axon Axon
Cerebral cortex (grey matter)
Postsynaptic
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Dendrites
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Axon
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Figure 4.3 A coronal slice of a human brain showing fissures and gyri, the layer of cerebral cortex that follows these convolutions and the white and grey matter. Source: Harvard Medical School/Betty G. Martindale.
Soma (cell body)
Axon
Myelin sheath
Terminal buttons
Figure 4.4 The principal parts of a neuron and its connections with other neurons (synapses).
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As we saw earlier, some nerves are attached to the spinal cord and others are attached directly to the brain. The spinal nerves, attached to the spinal cord, serve all of the body below the neck, conveying sensory information from the body and carrying messages to muscles and glands. The twelve pairs of cranial nerves, attached to the brain, serve primarily muscles and sense receptors in the neck and head. For example, when you taste food, the sensory information gets from your tongue to your brain through one set of cranial nerves. Other sets of cranial nerves bring sensory information to the brain from the eyes, ears and nose. When you chew food, the command to chew reaches your jaw muscles through another set of cranial nerves. Still other cranial nerves control the eye muscles, the tongue, the neck muscles and the muscles we use for speech.
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Neurons, or nerve cells, are the elements of the nervous system that bring sensory information yp to the brain, store memories, reach decisions sych and control the activity of the muscles. They are assisted in their task by another kind of cell: the glia. Glia (or glial cells) get their name from the Greek word for glue and 90 per cent of cells in the brain are glial cells. At one time, scientists thought that glia simply held neurons – the important elements of the nervous system – in place. They do not, however, literally stick neurons together but they do provide important physical support to neurons as well as providing other forms of mechanical support. During development of the brain, some types of glial cells form long fibres that guide developing neurons from their place of birth to their final resting place. Other types of glia manufacture chemicals that neurons need to perform their tasks and absorb chemicals that might impair neurons’ functioning. Others form protective insulating sheaths around nerve fibres. Still others serve as the brain’s immune system, protecting it from invading micro-organisms that might infect it. Research suggests that they may play a more important part in brain development than was originally thought. For example, one study has shown that glial cells may determine the number of junctions between neurons – called synapses – generated in the brain (Ullian et al., 2001). This finding followed an experiment by researchers from the same laboratory which found that synapses of neurons grown with a certain type of glial cell were ten times more active than those grown without. The mere proximity of glial cells to neurons made the neurons more responsive. In their most recent experiment, neurons that were exposed to glial cells formed seven times as many synapses as those that were not exposed. This is important because it indicates that glial cells have a much greater role to play in the formation of ee
synapses in the CNS than had previously been thought. The next step is to identify how the glial cells produce this increase. The four principal parts of a neuron are shown in Figure 4.4.
1 The soma, or cell body, is the largest part of the neuron and contains the mechanisms that control the metabolism and maintenance of the cell. The soma also receives messages from other neurons. 2 The dendrites, the tree-like growths attached to the soma, function principally to receive messages from other neurons (dendron means ‘tree’). They transmit the information they receive down their ‘trunks’ to the soma. 3 The nerve fibre, or axon, carries messages away from the soma towards the cells with which the neuron communicates. These messages, called action potentials, consist of brief changes in the electrical charge of the axon. For convenience, an action potential is usually referred to as the firing of an axon. 4 The terminal buttons are located at the ends of the ‘twigs’ that branch off the ends of axons. Terminal buttons secrete a chemical called a transmitter substance whenever an action potential travels down the axon, i.e. whenever the axon fires. These chemicals are called neurotransmitters. The transmitter substance affects the activity of the other cells with which the neuron communicates. Thus, the message is conveyed chemically from one neuron to another. Most drugs that affect the nervous system and hence alter a person’s behaviour do so by affecting the chemical transmission of messages between cells.
Neurotransmitters There are currently around 50 or so identifiable neurotransmitters and all are important to behaviour in some way. Some, however, play a greater role than others. The amine group of neurotransmitters, for example, which includes dopamine, noradrenaline and serotonin (5-hydroxytryptamine), appears especially important to psychologists because they are involved in a range of behaviours – emotional expression, decision-making, response to reward, inhibiting inappropriate actions, drug-taking and many others. A part of the brain, called the nucleus accumbens, appears to be part of a reward system in the front and midpart of the brain, which evaluates how salient or important events in the outside world are. It and the system it belongs to are also implicated in impulsive behaviour – the inability to delay reward and to be aware of the consequences of actions, and so on (Pothuizen et al., 2005). Drugs which act on serotonin receptors here, for example, increase impulsivity (Pattij and Vanderschuren,
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Many axons, especially long ones, are insulated with a substance called myelin. The white matter located beneath the cerebral cortex gets its colour from the myelin sheaths around the axons that travel through these areas. Myelin, which is part protein, part fat, is produced by special cells that individually wrap themselves around segments of the axon, leaving small bare patches of the axon between them. The principal function of myelin is to insulate axons from each other and thus to prevent the scrambling of messages. It also increases the speed of the action potential. In some cases, people’s immune systems go awry and begin to attack parts of their own bodies. One of these disorders is called multiple sclerosis – an autopsy of the brain and spinal cord will show numerous patches of hardened, damaged tissue (skleros is Greek for ‘hard’). The immune systems of people who have multiple sclero-
The action potential
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sis attack a protein in the myelin sheath of axons in the central nervous system, stripping it away. Although most of the axons survive this assault, they can no longer function normally, and so, depending on where the damage occurs, people who have multiple sclerosis suffer from various sensory and motor impairments. There is also evidence to suggest that the central nervous system becomes fully mature when myelination is complete; speed of information processing in children, for example, seems to mirror cortical development and ongoing myelination (Travis, 1998).
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yp The message carried by the axon – the action sych potential – involves an electrical current, but it does not travel down the axon the way electricity travels through a wire. Electricity travels through a wire at hundreds of millions of metres per second. The axon transmits information at a much slower rate – less than 100 metres per second. The membrane of an axon is electrically charged. When the axon is resting (that is, when no action potential is occurring), the outside is charged at +70 millivolts (mV, thousandths of a volt) with respect to the inside. An action potential is an abrupt, short-lived reversal in the electrical charge of an axon. This temporary reversal begins at the end of the axon that attaches to the soma and is transmitted to the end that divides into small branches capped with terminal buttons. The electrical charge of the axon occurs because of an unequal distribution of positively and negatively charged particles inside the axon and in the fluid that surrounds it. These particles, called ions, are produced when various substances – including ordinary table salt – are dissolved in water. Normally, ions cannot penetrate the membrane that surrounds axons. However, the axonal membrane contains special submicroscopic proteins that serve as ion channels or ion transporters. Ion channels can open or close; when they are open, a particular ion can enter or leave the axon. Ion transporters work like pumps. They use the energy resources of the cell to transport particular ions into or out of the axon, as seen in Figure 4.5. The outside of the membrane is positively charged (and the inside is negatively charged) because the axon contains more negatively charged ions and fewer positively charged ions. When an axon is resting, its ion channels are closed, so ions cannot move into or out of the axon. An action potential is caused by the opening of some ion channels in the membrane at the end of the axon nearest the soma. The opening of these ion channels permits positively charged sodium ions to enter, which reverses the membrane potential at that location. This reversal causes nearby ion channels to open, which produces another b
2008). Such impulsivity, according to some scientists, is linked to the initiation and maintenance of drug-seeking (Krishnan-Sarin et al., 2007). The events the nucleus accumbens responds to can include rewarding stimuli (food, water, sex), aversive stimuli (ice, shock) and novel stimuli. Dopamine release increases here, as does the firing of dopamine receptors when an organism is rewarded with food or water (Schultz, 2007; Iversen and Iversen, 2007). Dopamine can increase by as much as 20–100 per cent and last for up to 100 minutes (Schultz, 2007). If an organism expects a reward there is a release of dopamine in these regions, but if an organism is completely rewarded there seems to be little dopamine activation. Dopamine is also released in freely moving organisms, which suggests that it is important for motor movement and the motivation to move. Of course, the movement disorder Parkinson’s disease, discussed a little later, is treated by a dopamine precursor (called Levodopa), and excessive dopamine is thought to be implicated in some of the symptoms of schizophrenia (described in Chapter 18). Like all the amines, dopamine receptors begin projecting from the brain stem and certain dopamine receptors terminate (end their projections) in the front part of the brain (called the prefrontal cortex, described below). These receptors, called D1 receptors, appear to be very important to cognitive performance and influence tasks such as our ability to store and manipulate non-verbal information over very short periods of time (a type of memory called working memory, described in Chapter 8). Some people have a mutation of an allele which directly affects dopamine (by inactivating it) with the consequence that their cognitive function is impaired (Turbridge et al., 2006). Another type of dopamine receptor, D2, seems to be reduced in the striatum of drug addicts (Kalivas and Volkow, 2005).
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Action potential travels in this direction
3. Ion transporters pump sodium and potassium ions back to their original locations
Inside of axon
Outside of axon
Ion transporters actively pump ions in or out of axon
Closed ion channels prevent ions from entering or leaving axon
Figure 4.5 Ion channels and ion transporters. These structures regulate the number of ions found inside and outside the axon. An unequal distribution of positively and negatively charged ions is responsible for the axon’s electrical charge.
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Neurons communicate with other cells by yp sych means of synapses. A synapse is the conjunction of a terminal button of one neuron and the membrane of another cell – neuron, muscle cell or gland cell. The terminal button belongs to the presynaptic neuron – the neuron that sends the message. When terminal buttons become active, they release a chemical called a transmitter substance. The neuron that receives the message (detects the transmitter substance) is called the postsynaptic neuron. A neuron receives messages from many terminal buttons, and in turn its terminal buttons form synapses with many other neurons. The drawing in Figure 4.4 is much simplified; thousands of terminal buttons can form synapses with a single neuron. Figure 4.7 illustrates the relation between a motor neuron and a muscle. A motor neuron is one that forms synapses with a muscle and controls its contractions. When the axon of a motor neuron fires, all the muscle fibres with which it forms synapses will contract with a brief twitch. A muscle consists of thousands of individual muscle fibres. It is controlled by a large number of motor neurons, each of which forms synapses with different groups of muscle fibres. The strength of a muscular contraction, then, depends on the rate of firing of the axons that control it. If they fire at a high rate, the muscle contracts forcefully; if they fire at a low rate, the muscle contracts weakly. b
Open ion channels permit ions to enter or leave axon
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Figure 4.6 Movement of sodium and potassium ions during the action potential. Sodium ions are represented by orange arrows, potassium ions by green arrows.
Synapses Ions
1. Sodium channels open; sodium ions enter, reversing membrane potential
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reversal at that point. The process continues all the way to the terminal buttons located at the other end of the axon. Note that an action potential is a brief reversal of the membrane’s electrical charge. As soon as the charge reverses, the ion channels close and another set of ion channels opens for a short time, letting positively charged potassium ions out of the axon. This outflow of positive ions restores the normal electrical charge. Thus, an action potential resembles the ‘Mexican wave’ that football fans often make in a stadium. People in one part of the stadium stand up, raise their arms over their heads, and sit down again. People seated next to them see that a wave is starting, so they do the same – and the wave travels around the stadium. Everyone remains at the same place, but the effect is that of something circling in the stands around the playing field. Similarly, electricity does not really travel down the length of an axon. Instead, the entry of positive ions in one location reverses the charge at that point and causes ion channels in the adjacent region to open, and so on, as seen in Figure 4.6. The ion transporters pump sodium ions out of the axon and pump potassium ions back in, restoring the normal balance.
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Figure 4.7 Synapses between terminal buttons of the axon of a motor neuron and a muscle.
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There are broadly two types of synapse: excitatory synapses and inhibitory synapses. yp Excitatory synapses do just what their name sych implies. When the axon fires, the terminal buttons release a transmitter substance that excites the postsynaptic neurons with which they form synapses. The effect of this excitation is to make it more likely that the axons of the postsynaptic neurons will fire. Inhibitory synapses do just the opposite. When they are activated, they lower the likelihood that the axons of the postsynaptic neurons will fire. The rate at which a particular axon fires is determined by the activity of the synapses on the dendrites and soma of the cell. If the excitatory synapses are the more active, the axon will fire at a high rate. If the inhibitory synapses are the more active, the axon will fire at a low rate or perhaps not at all, as seen in Figure 4.8. How do molecules of transmitter substance exert their excitatory or inhibitory effect on the postsynaptic neuron? When an action potential reaches a terminal button, it causes the terminal button to release a small amount of transmitter substance into the synaptic cleft, a fluid-filled space between the terminal button and the membrane of the postsynaptic neuron. The transmitter substance causes ee
reactions in the postsynaptic neuron that either excite or inhibit it. These reactions are triggered by special submicroscopic protein molecules embedded in the postsynaptic membrane called receptor molecules (see Figure 4.9). A molecule of a transmitter substance attaches to a receptor molecule the way a key fits in a lock. After their release from a terminal button, molecules of transmitter substance find their way to the receptor molecules, attach to them and activate them. Once they are activated, the receptor molecules produce excitatory or inhibitory effects on the postsynaptic neuron. They do so by opening ion channels. The ion channels found at excitatory synapses permit sodium ions to enter the neuron; those found at inhibitory synapses permit potassium ions to leave it (see Figure 4.10). The excitation or inhibition produced by a synapse is short-lived; the effects soon pass away, usually in a fraction of a second. At most synapses, the effects are terminated by a process called reuptake. The transmitter substance is released by the terminal button and is quickly taken up again. It has, therefore, only a short time to stimulate the postsynaptic receptor molecules, as you can see from Figure 4.11. The rate at which the terminal button takes back the transmitter substance determines how prolonged the effects of the chemical on the postsynaptic neuron will be. The faster the transmitter substance is taken back, the shorter its effects will be on the postsynaptic neuron. As we will see, some drugs affect the nervous system by slowing down the rate of reuptake, thus prolonging the effects of the transmitter substance.
Axon of excitatory neuron
Excitatory effects (red)
Axon of inhibitory neuron
Action potentials occur when enough excitation reaches this location
Inhibitory effects (blue)
Figure 4.8 Interaction between the effects of excitatory and inhibitory synapses. The rate of firing of the axon of the neuron is controlled by these two factors.
h syc la
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THE NERVOUS SYSTEM: THE BRAIN AND ITS COMPONENTS Closed ion channel Presynaptic membrane
Synaptic cleft
Open ion channel
Molecule of transmitter substance
Terminal button
Receptor molecule
Receptor molecule
Postsynaptic membrane Closed ion channel
Open ion channel
Figure 4.10 Detailed view of receptor molecules in the postsynaptic neuron. When activated by molecules of a transmitter substance, the receptor molecules allow sodium ions to enter the postsynaptic neuron, causing excitation, or allow potassium ions to leave, causing inhibition.
Postsynaptic membrane
Molecule of transmitter substance being released Activation of receptor molecules has excitatory or inhibitory affect on postsynaptic neuron
Activation of receptor molecules has excitatory or inhibitory effect on postsynaptic neuron
Receptor molecule activated by transmitter substance
Receptor molecule activated by transmitter substance
Reuptake: molecule of transmitter substance being taken back into terminal button
Figure 4.9 The release of a transmitter substance from a terminal button. Top: Before the arrival of an action potential. Middle: Just after the arrival of an action potential. Molecules of transmitter substance have been released. Bottom: Activation of receptor molecules. The molecules of transmitter substance diffuse across the synaptic cleft and some of them activate receptor molecules in the postsynaptic membrane.
Terminal button
Figure 4.11 Reuptake of molecules of transmitter substance.
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A simple neural circuit The interconnections of the billions of neurons in our central nervous system provide us with the capacities for perception, decision-making, memory and action. It has been estimated that there are 13 trillion such connections. Although we do not yet know enough to draw a ‘neural wiring diagram’ for such complex functions, we can do so for some of the simpler reflexes that are triggered by certain kinds of sensory stimuli. For example, when your finger touches a painfully hot object, your hand withdraws. When your eye is touched, your eyes close and your head draws back. When a baby’s cheek is touched, it turns its mouth towards the object, and if the object is of the appropriate size and texture, the baby begins to suck. All these activities occur quickly, without thought. A simple withdrawal reflex, which is triggered by a noxious stimulus (such as contact with a hot object), requires three types of neuron. Sensory neurons detect the noxious stimulus and convey this information to the spinal cord. Interneurons, located entirely within the brain or spinal cord, receive the sensory information and in turn stimulate the motor neurons that cause the appropriate muscle to contract, as seen in Figure 4.12. The sequence is simple and straightforward. A noxious stimulus applied to the skin produces a burst of action
potentials in the sensory neurons. Their axons fire, and their terminal buttons, located within the spinal cord, release an excitatory transmitter substance. The chemical stimulates the interneurons and causes them to fire. The interneurons excite the motor neurons, and these neurons cause the muscle to contract. The next example adds a bit of complexity to the circuit. Imagine that you have removed a hot casserole dish from the oven. As you move over to the table to put it down, the heat begins to penetrate the rather thin ovengloves you are using. The pain caused by the hot dish triggers a withdrawal reflex that tends to make you drop it. And yet you manage to keep hold of it long enough to get to the table and put it down. What prevented your withdrawal reflex from making you drop the dish on the floor? As you saw earlier, the activity of a neuron depends on the relative activity of the excitatory and inhibitory synapses on it. The pain from the hot casserole dish increases the activity of excitatory synapses on the motor neurons, which tends to cause the hand to open. However, this excitation is counteracted by inhibition from another source – the brain. The brain contains neural circuits that recognise what a disaster it would be if you dropped the casserole dish on the floor. These neural circuits send information to the spinal cord that prevents the withdrawal reflex from making you drop the dish. Figure 4.13 shows how this information
Brain
Spinal cord
This interneuron excites motor neuron, causing muscular contraction
Motor neuron
This muscle causes withdrawal from source of pain Axon of sensory neuron (pain)
Cross-section of spinal cord
Figure 4.12 Schematic representation of the elements of a withdrawal reflex. Although this figure shows just one sensory neuron, one interneuron and one motor neuron, in reality many thousands of each type of neuron are involved.
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reaches the spinal cord. As you can see, an axon from a neuron in the brain reaches the spinal cord, where it forms a synapse with an inhibitory interneuron. When the neuron in the brain becomes active, it excites this inhibitory interneuron. The interneuron releases an inhibitory transmitter substance, which decreases the rate of firing of the motor neuron, preventing your hand from opening. This circuit provides an example of a contest between two competing tendencies: to drop the casserole dish and to hold onto it. Complex decisions about behaviour are made within the brain by much more complicated circuits of neurons, but the basic principles remain the same.
Neuromodulators: action at a distance Terminal buttons excite or inhibit postsynaptic neurons by releasing transmitter substances. These chemicals travel a very short distance and affect receptor molecules located on a small patch of the postsynaptic membrane. But some neurons release chemicals that get into the general circulation of the brain and stimulate receptor molecules on many thousands of neurons, some located a considerable distance away. The chemicals these neurons release are called neuromodulators, because they modulate the activity of the neurons they affect. We can think of neuromodulators as the brain’s own ‘drugs’. Because these chemicals diffuse widely in the
brain, they can activate or inhibit many different circuits of neurons, thus exerting several behavioural and physiological effects. These effects act together to help achieve a particular goal. The best-known neuromodulator is a category of chemicals called endorphins, or opioids (‘opium-like substances’). Opioids are neuromodulators that stimulate special receptor molecules (opioid receptors) located on neurons in several parts of the brain. Their behavioural effects include decreased sensitivity to pain and a tendency to persist in ongoing behaviour. Opioids are released while an animal is engaging in important species-typical behaviours, such as mating or fighting. The behavioural effects of opioids ensure that a mating animal or an animal fighting to defend itself is less likely to be deterred by pain; thus, conception is more likely to occur and a defence is more likely to be successful. Many years ago, people discovered that eating or smoking the sap of the opium poppy decreased their sensitivity to pain, so they began using it for this purpose. They also discovered that the sap produced pleasurable effects: people who took it enjoyed the experience and wanted to take more. In recent times, chemists have discovered that the sap of the opium poppy contains a class of chemicals called opiates. They also learned how to extract and concentrate them and to produce synthetic versions with even greater potency. In the mid-1970s, neurobiologists learned that opiates produce their effect
Neuron in brain Brain Axon of neuron in brain Spinal cord
This interneuron excites motor neuron, causing muscular contraction
Axon from neuron in brain
Motor neuron
This muscle causes withdrawal from source of pain Axon of sensory neuron (pain)
Cross-section of spinal cord This interneuron inhibits motor neuron, preventing muscular contraction
Figure 4.13 Schematic representation of a withdrawal reflex being inhibited by the brain.
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by stimulating special opioid receptor molecules located on neurons in the brain (Pert et al., 1974). Soon after that, they discovered the brain’s opioids (Terenius and Wahlström, 1975). Thus, opiates mimic the effects of a special category of neuromodulators that the brain uses to regulate some types of species-typical behaviours. The brain produces other neuromodulators. Some help organise the body’s response to stress, while others reduce anxiety and promote sleep. Some promote eating, while others help end a meal.
Techniques in psychobiology and neuroscience Until relatively recently, most of our knowledge of the functions of the nervous system was obtained through research using laboratory animals. This research produced important discoveries about the causes and treatments of neurological and mental disorders, many of which are discussed in this book. It led to the development of drugs and surgical techniques that help people with neurological disorders, such as Parkinson’s disease, and mental disorders, such as schizophrenia, depression and obsessive-compulsive disorders. Physiological psychologists now have at their disposal a range of research methods to study the function of the brain and body that would have been impossible to imagine just a few decades ago. We have ways to identify neurons that contain particular chemicals. We have ways to take photographs of particular ions entering neurons when the appropriate ion channels open. We have ways to inactivate individual genes to see what happens to behaviour when they no longer function. We can also witness the activity of the brain as it behaves, through the technique of neuroimaging.
Lesioning The earliest of research methods in psychobiology – and one that is still the most commonly used – involves correlating a behavioural deficit with damage to a specific part of the nervous system. The damage can be studied in one of two ways. For example, a neuropsychologist may examine the effects of brain damage on function, such as the effect of damage to the front part of the brain on a person’s ability to create and adhere to plans. The second way involves the investigator producing an experimental brain lesion, an injury to a particular part of the brain, but only in an animal’s brain. Of course, neurosurgeons do lesion parts of the brain to alleviate some forms of suffering. One recent, successful treatment for the movement disorder Parkinson’s disease, for example, has
involved lesioning a small structure deep within the brain. A similar technique ‘lesions’ in another way (the procedure is called deep brain stimulation, DBS). In Parkinson’s disease, a person may behave rigidly or be unable to walk properly or exhibit tremors or engage in excessive, repetitive, involuntary motor behaviour. Treatment by Levodopa (mentioned earlier) provides some respite but there are off periods when the drug does not work. DBS overstimulates parts of a collection of structures called the basal ganglia, described below. This has been found to be more successful than lesioning the parts directly (Liu et al., 2008). Why lesioning and overstimulation seem to work (i.e. produce the same effect) is still a mystery. One theory is that surgery reduces the inhibitory effects of neurons in the basal ganglia and increases them in another structure, the thalamus and cortex (Liu et al., 2008). When an animal’s brain is experimentally lesioned, the investigator hypothesises that this lesion might have specific consequences; they then study the effects of the lesion on the animal’s behaviour. If particular behaviours are disrupted, the reasoning suggests, the damaged part of the brain must be involved in those behaviours. Some lesioning techniques are used in both experimental and neurosurgical work. For example, to reach the region to be lesioned, the experimenter or surgeon uses a device called a stereotaxic apparatus to insert a fine wire (called an electrode) into a particular location in the brain, as Figures 4.14 and 4.15 show. The term ‘stereotaxic’ refers to the ability to manipulate an object in three-dimensional space. The researcher passes an electrical current through the electrode, which produces heat that destroys a small portion of the brain around the tip of the electrode. After a few days, the animal recovers from the operation, and the researcher can assess its behaviour. A stereotaxic apparatus can also be used to insert wires for recording the electrical activity of neurons in particular regions of the brain. But an electrode placed in an animal’s brain can also be used to lead electrical current into the brain as well as out of it. If an electrical connector on the animal’s skull is attached to an electrical stimulator, current can be sent to a portion of the animal’s brain. This current activates neurons located near the tip of the electrode. The experimenter can then see how this artificial stimulation affects the animal’s behaviour. Neurosurgeons sometimes use stereotaxic apparatus to operate on humans. For example, as you read earlier, destruction of a particular region near the centre of the cerebral hemispheres can alleviate the tremors (trembling) that occur in some cases of Parkinson’s disease (Krack et al., 1998; Samuel et al., 1998) (see Figure 4.16). Neurosurgeons can also insert electrodes into the human brain and record the electrical activity of particular regions to try to find locations that might be responsible for triggering epileptic seizures.
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Connecting socket
Dental cement
Electrodes Adjusting knobs
Skull
Brain Skull
Figure 4.15 A permanently attached set of electrodes in an animal’s brain and a connecting socket cemented to the skull.
Electrode in brain
Figure 4.14 A stereotaxic apparatus, used to insert a wire into a specific portion of an animal’s brain.
(a)
(b)
Figure 4.16 (a) Shows the typical stereotaxic set-up in surgery designed to reduce symptoms of Parkinson’s disease. (b) Fergus Henderson, celebrated chef of the St John restaurant in London. Henderson suffered from Parkinson’s disease until he received surgery to control the symptoms. His hands are in his pockets because he could not keep them still when this photograph was taken. Source: (a) BSIP, Astier/Science Photo Library Ltd.; (b) © John Reardon, www.abbyjohnston.com.
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Studying brain injury: clinical neuropsychology Although we can, under very careful conditions, experimentally lesion the brains of non-humans, we cannot do this in humans, for very obvious reasons. We have, therefore, relied on studies of accidental brain injury to help us build a picture of the role of damaged brain regions in specific functional impairments. This approach usually utilises the single-case study design, described in Chapter 2. Brain injury usually results from accident or disease and, because it is more difficult to obtain information of this kind, scientists have studied a small number of individuals intensively over a long period of time. The approach allows neuroscientists to observe how fairly localised brain damage can impair intellectual or emotional function. Most human brain lesions are the result of natural causes, such as a stroke. A stroke (also known as a cerebrovascular accident, or CVA) occurs when a blood clot obstructs an artery in the brain or when a blood vessel in the brain bursts open. In the first case, the clot blocks the supply of oxygen and nutrients to a particular region and causes that region to die. In the second case, the blood that accumulates in the brain directly damages neural tissue, partly by exerting pressure on the tissue and partly through its toxic effects on cells. The most common causes of strokes are high blood pressure and high levels of cholesterol in the blood. We consider these factors and their effect on health in Chapter 17. The brain injury in such patients has given rise to a large number of neuropsychological disorders which have helped shape theories of cognitive function. These disorders include the inability to produce or comprehend speech (aphasia), inability to produce speech (fluent or Broca’s aphasia), inability to comprehend speech, specifically (Wernicke’s aphasia), inability to recognise objects (agnosia), inability to follow motor commands (apraxia), reading impairment (acquired dyslexia), inability to recognise familiar faces (prosopagnosia), inability to attend to stimuli in one half of the visual field (spatial neglect), and a lack of awareness of visual objects, among many others (and you will read more about them in later chapters). Other impairments have no specific name but involve an inability to perform a specific function, such as recognising specific emotions in faces and voices; placing events in sequence; planning; learning new material or retrieving old material from memory. One of the most famous – if not the most famous – single-case study in neuropsychology is HM. You will find more about HM in the chapter on memory but, briefly, HM underwent surgery for uncontrollable epilepsy in the late 1950s. The surgery involved removal of a part of the brain called the temporal lobe which includes a structure called the hippocampus (this has been implicated in various
memory functions). After the surgery and beyond, HM exhibited a form of memory impairment called anterograde amnesia – he was unable to learn new material. The intensive study of HM led to a neurobiological theory of human memory which involved the temporal lobe and the hippocampus and the study has since been supplemented by other case studies and neuroimaging studies of memory in healthy participants. There have been arguments for and against the singlecase study approach in neuropsychology. Some researchers argue that damage to a brain region does not necessarily demonstrate that this region is responsible for any function that is disrupted following injury. Other areas connected to the damaged region may be responsible for the specific function but connections to the intact areas from the lesioned area have been disrupted. There is also the need to specify exactly what function is being measured (this is a problem for psychology in general, rather than neuropsychology in particular). When we say that a region may be ‘responsible’ for phonological processing, what exactly is meant by phonological processing? Could the region be responsible for some other function which allows phonological processing, rather than being responsible for phonological processing itself? There are also obvious methodological and practical problems such as the extent and locus of the lesion – because the brain injury is accidental or the result of a disease, the extent of damage is uncontrollable. There is also great variation in regional brain structure between individuals. Amunts et al. (1999), for example, found that the size of Broca’s area varied enormously in a group of ten individuals: there was a tenfold difference between participants in some cases. When such injury occurs it is also unlikely to be limited to one specific region or structure; it may extend to more than one and so conclusions drawn about the significance of findings in studies such as these need to be done circumspectly. There are also other factors such as sex, personality, handedness and intellectual ability which may need to be taken into account.
Rehabilitation after brain damage Rehabilitation is an ‘active process whereby people who are disabled by injury or disease work together with professional staff, relatives and members of the wider community to achieve their optimum physical, psychological, social and vocational well-being’ (McLellan, 1991, p. 785) and programmes have been designed for reading disorders resulting from brain injury (acquired reading disorders) (Patterson, 1994), the inability to produce or understand speech (aphasia) (Berndt and Mitchum, 1995), an inability to attend to or ‘see’ one half of the world (spatial neglect) (Robertson et al., 1993) and memory disorders (Wilson and Powell, 1994; Glisky, 1997).
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The Top Gear television presenter Richard Hammond, crashed his car while attempting to break the British land-speed record. His jet-powered vehicle was travelling at 314 mph when a tyre burst. Hammond was hospitalised with brain injury. Although he made a good physical recovery, he still reports periods of severe depression, emotional problems such as becoming angry or scared and not knowing how to cope with these states, and short-term memory loss, including forgetting the PINs of his credit cards. Source: Alamy Images/Mirrorpix
The most common type of rehabilitation programme is cognitive rehabilitation (Parente and Stapleton, 1997). In this, the patient is encouraged to engage in two types of activity: (1) ‘the reinforcing, strengthening or establishing of previously learned behaviour’, and (2) the establishment of ‘new patterns of cognitive activity or mechanisms to compensate’ for the impairment (Bergqvist and Malec, 1997). It shows consistently successful results in the majority of cases of mild to severe brain injury (Ho and Bennett, 1997). A common form of impairment following brain injury is memory disorder. Specific problems include deficits in
learning new material and in retaining other kinds of information (Wilson and Powell, 1994). Some techniques of rehabilitation used to improve memory include exercises and drills, use of external aids, and the use of mnemonic strategies. The patients ‘JC’ and Julia Cogan are good examples of how rehabilitation strategies can work effectively in reducing problems in everyday life in individuals with severe memory impairment (Wilson, 1991, 1995; Wilson et al., 1997; Oddy and Cogan, 2005). JC, for example, is a self-employed French-polisher who, during the second year at university, suffered an epileptic seizure and collapsed during a tutorial. Doctors, family and friends noted that JC showed severe loss of memory and could not remember anything ‘from one minute to the next’. JC used external aids, such as a diary or notebook, mnemonics and chaining – where tasks are broken down into smaller steps or stages and which can, for example, help patients to find their way around when planning short journeys. These benefited JC but were developed by him into a more elaborate strategy: he has been using and refining this strategy for at least 10 years following his impairment. During the early stages, he began to use a pocketbook kept in his shirt and used a watch with an alarm that sounded every hour – he would note what he was doing in his notebook when this sounded (Wilson et al., 1997). He would create weekly and daily sheets on which he would write down all appointments and lists of things to do or done. He bought a Dictaphone whose content he would transcribe at the end of everyday. His aunt noted how a new watch helped him because it was capable of 15 programmed weekly alarms and 15 one-off alarms. He would use the one-off alarms for reminding him of individual events. He would role-play some social situations to avoid the embarrassment of not being able to remember in public. He would make a log of all phone calls so that he didn’t ring someone twice with the same message. JC’s success is mirrored by that of Julia Cogan, a 23year-old first class graduate in physics who was studying for a Ph.D. in neuroimaging and oncology when she suffered brain injury (Oddy and Cogan, 2005). She made a full physical recovery but her memory was severely impaired. Her everyday problems are familiar ones; she is unable to remember what she had for breakfast, for example, and relies on the strategies she has developed so that she can lead as normal a life as possible. Like JC, she makes extremely good use of her Filofax and if she cannot remember a piece of information, she can find it quickly in her pad. The pad has extensive notes on people she’s met, her travel arrangements, recipes and so on (you can see an example in Figure 4.17). If she is asked how work is going, she can flick to a page which describes her last assignment and her next. Julia is young, well motivated, intelligent and very well organised. All of these characteristics can make rehabilitation easier.
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Figure 4.17 An example of the detailed timetable constructed by Julia Cogan to help her remember her travel arrangements. Source: Figure provided by kind permission of Julia Cogan and Professor Michael Oddy.
Psychology in action – Using brain activity to overcome physical disability A man in a wheelchair looks at a computer monitor. His arms and legs are still. He cannot speak. Without moving a limb, limbs which cannot move, he is able to move a cursor – not quickly, not effortlessly, but demonstrably – on the screen in front of him. Laboriously, but not without motivation, he spells out a word. In what seems like a vignette from the most trite science fiction fantasy, he is using the electrical potentials generated by his brain to guide the cursor. This, however, is no third-rate SF make-believe. It is an example of real technology in action: brain–computer interface (BCI). BCI is a method of controlling electronic or mechanical devices using brain activity. This is useful for people who have suffered illnesses which render them incapable of basic motor behaviour and for whom traditional types of assistive technology are inappropriate because they rely on voluntary motor movement. People who are paralysed, for example, might restore very basic movement through the manipulation of muscles or external devices via signals generated by the brain (Birbaumer, 2006). Those who might benefit include people with amyotrophic lateral sclerosis (ALS) who require artificial respiration and live in a completely ‘locked in’ state, multiple sclerosis, cerebral palsy, stroke, muscular dystrophy and brain injury who have a severe motor disability/paralysis. The first
of these ‘neural prostheses’ was inserted into the brain of a patient by US surgeon, Philip R. Kennedy, and his team in 1996. The patient was a teacher and artist who had been paralysed (Kennedy and Bakay, 1998). Two months after the surgery, he had learned how to turn lights on and off (Brown, 2008). A second patient eventually learned to pick out icons on a computer screen and to spell out a small number of words. Figures 4.18 a and b show you a patient in receipt of BCI and a schematic representation of the process. It is based on the the non-invasive recording of electrical activity (EEG) from the brain’s neurons. A person can be trained to use and alter this EEG activity to effect simple changes in motor behaviour. The EEG is ‘translated’ into output such as moving a cursor around a monitor to indicate ‘yes’ or ‘no’ to produce a certain change in the environment, such as switching a light on or off or turning the temperature up or down, spelling out the letters of a word on a monitor, sending an email, accessing the internet, opening and closing a prosthetic hand, or operating a wheelchair (Birbaumer et al., 2007; Daly and Wolpaw, 2008; Pfurtscheller et al., 2003a, b). Research has also found that by changing the appearance of certain types of EEG rhythm, patients can control their epileptic seizures (Sterman, 1981). According to Birbaumer (2006), extensive training can lead to almost 100 per cent control over these seizures.
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Psychology in action – Continued
Figure 4.18 (a) Dr Phil Kennedy, one of the pioneers of BCI technology, with one of his patients (Kennedy is in the blue shirt).
Figure 4.18 (b) A diagram showing the stages and processes involved in brain computer interface.
Source: Landor Media: David Kamerman/The Boston Globe
Source: University of Florida: Arturo Sinclair
The process involves two stages. The first is feature extraction and this involves the identification of the type of signal – its rhythm and amplitude, the neuron’s firing rate – that will influence output. The second involves using an algorithm which translates these signals into commands which specify outputs – the selection of letters, the movement of a cursor, etc. The patient might use the beta rhythm recorded over the sensorimotor cortex to make a movement. The algorithm takes into account that activity in a certain EEG frequency range should enable the person to move a cursor to left or right of a monitor. With repeated training and practice, the process becomes less
‘effortful’ and becomes automatic, in the way that many initially difficult behaviours become automatic with practice. That said, despite advances in technology and research, the advances are impressive but modest – typing on screen amounts to three to four words per minute, for example. Currently, these techniques are also vision-based: people must be able to see and need to maintain gaze for the technology to work but auditory versions are now being investigated (Nijboer et al., 2008). It is an unusual and innovate way of harnessing the power of the brain.
Psychophysiology: measuring CNS activity When psychobiologists record brain electrical activity from deep inside the structure, the technique is invasive, i.e. it invades some part of the body (in this case, the brain). Recording the electrical activity of neurons, for example, may involve inserting electrodes into the brain. However, electrical activity of neurons can also be recorded from the scalp non-invasively. Both methods involve a technique called electroencephalography (EEG), the recording of the brain’s electrical impulses. Electrodes attached to the scalp can record the activity of groups of millions of neurons (Andreassi, 2001; Martin, 2006). The number of electrodes used in brain research tends to be at the discretion of the experimenter. Some use two or three, others use a lot more (over one hundred in some cases), but in all cases researchers use a map showing where each elec-
trode should be placed on the scalp. This avoids errors and inconsistencies in the application of electrodes. EEG activity is seen in the form of a line-tracing or electroencephalogram (EEG or ‘brainwave’), although some modern EEG recording machines allow the conversion of EEG data into ‘brainmaps’ – these are two-dimensional representations of the EEG activity. They can be coloured or in greyscale which means that areas of high and low activity can be represented by darker or lighter colours. There are different types of EEG waves – called frequencies – and these are thought to represent different psychological states. Some large, slow EEG waves, for example, are characteristic of deep sleep. One type of activity, called alpha, is the resting adult EEG; when we are engaged in thinking or making rapid movements, alpha activity changes to another type of activity (Andreassi, 2001). In Chapter 9, you will see how different types of EEG brain activity occur during different stages of sleep and wakefulness.
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One benefit of the EEG technique is that, as well as being non-invasive, it provides a measure of the brain’s activity in real time, as it happens. We can, therefore, match the presentation of a stimulus or a task with the brain activity associated with it. In this way, we can measure how the brain responds while it is engaged in tasks such as deciding whether two figures rotated in three-dimensional space are the same or different (Williams et al., 1995), watching pleasant or unpleasant visual stimuli (Davidson, 1992), smelling food odour (Martin, 1998) or recognising faces and words (Burgess and Gruzelier, 1997), among many other behaviours. Sometimes, however, this electrical signal can be messy or noisy: it is difficult to distinguish between the brain’s normal background activity and the activity produced by the perception of, or response to, a stimulus. The effect of perceiving a sound, for example, may be so small as to be invisible in an EEG tracing. To overcome this, psychophysiologists have devised the technique of averaging signals across trials. They can do this by recording eventrelated potentials or ERPs (these are sometimes also called evoked potentials). These are electrical signals recorded to a repeatedly presented stimulus (or set of stimuli). Each EEG response to a stimulus is added and averaged to produce one clearer signal or evoked potential. The potentials are event-related because they are related to a specific event that is external or internal to the individual such as decision-making (internal stimulus) or perceiving a flash of light (external stimulus). The point of averaging is to make the effect of a stimulus on the EEG clearer; background noise is reduced and the effect of the stimulus becomes more obvious. Some ERPs measure sensory responses to stimuli (this is called the N100 (or N1), so called because it appears 100 milliseconds after the onset of a stimulus), others are thought to be associated with more cognitive functions such as understanding words or being able to distinguish one type of visual or auditory stimulus from another. These ERPs occur later, at around 300 or 400 milliseconds after stimulus onset (the P300 or P3 and N400 or N4), perhaps reflecting the time the brain takes to undertake these cognitive operations (Polich and Kok, 1995). The N400, for example, was the first ERP to be specifically linked with language processing and is elicited when participants read sentences in which the last word is semantically surprising or inappropriate, although linguistically legal (Kutas and Hillyard, 1980). For example, the sentence, ‘A man who has lost ninety per cent of his brain is called a widower’ is legal but surprising whereas the sentence, ‘A man who has lost ninety per cent of his brain is called a zombie’ is legal but not surprising. The amplitude of the N400 is associated with processing difficulty such that the more difficult the task, the greater the amplitude of the N400 (Kutas and Van Petten, 1994). The N400
declines when congruous sentences are presented – the last word is predictable – but not when incongruous ones are presented (Van Petten and Kutas, 1990). Some researchers have suggested that the N400 reflects a difficulty in integrating words into a sentence (Kutas et al., 2000): the greater the difficulty, the larger the N400. ERPs have been used to investigate a number of psychological functions such as decision-making, sentence comprehension, recognition memory and visual, tactile and auditory perception. They are not as good as other techniques at localising activity to a specific brain area but they are good at measuring responses to stimuli in real time. The absence of an evoked potential indicates an impairment in function or a failure to attend to stimuli. Figure 4.19 shows the difference between ERPs evoked by a decision-making task in healthy volunteers and individuals with dementia. Note the reduction in the amplitude (size) of the wave in the demented group.
Psychophysiology: measuring activity outside the CNS Psychophysiologists can also record electrical activity in the peripheral (or autonomic) nervous system – from the heart, muscles and skin. Some of the most common techniques are EMG, ECG and GSR.
Electromyography (EMG) The body possesses three types of muscles – skeletal, smooth and cardiac. Skeletal muscles are those such as biceps, triceps and flexor muscles of the upper arm and forearm. These are usually under voluntary control – they make up the voluntary motor system; we decide when to flex and tense our arms (such as when picking up a cup), legs (kicking a ball) or fingers (writing or typing at a keyboard). There are other muscles which are not under voluntary control. Smooth muscles are those over which we have little or no voluntary control – the constriction and dilation of blood vessels, for example. The third type of muscle is cardiac and, as the name suggests, this muscle makes up the heart and its valves. Smooth and cardiac muscles comprise about 10 per cent of total body weight; the skeletal muscles make up around 40 per cent of this weight. When the muscles of the body contract, they generate electrical potentials. Often, muscles contract for psychological reasons – responding to stress, emotional stimuli, pictures, sounds, faces, and so on – and they sometimes contract for these reasons in ways that are undetectable to the eye. The technique used for measuring skeletal muscles’ electrical activity is electromyography (EMG). EMG activity is recorded by electrodes – circular disks of around 10 mm in diameter – from the surface of the skin. The greater the muscle contraction and the closer the elec-
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Alzheimer’s patients Normal controls
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Figure 4.19 Examples of EPs measured in healthy individuals and those with Alzheimer’s disease. When a participant is asked to undertake a task such as detecting the number of low tones in a series of high and low tones (where there are always fewer low tones), the ERPs illustrated here are found. The waves on the right show the brain’s response to the high tones (the common ones); the N1 sensory and P2 components can be clearly seen. However, when the participant has to make a decision (discriminating between high and low tones) a late wave – the P3 – appears in response to the low tones (the rarer ones). This wave is thought to reflect the brain’s decisionmaking processes. Note how the amplitude (height) of the P3 is lower than that seen in healthy individuals.
trode is to the skin, the greater the electrical activity generated (in fact, EMG records activity from motor units just prior to muscle contraction). For example, imagine a simple behaviour such as gripping an object like a hammer or a handle. The harder you grip the object, the greater the electrical activity produced by musculature and this activity can be picked up as EMG activity from the recording electrode. Imagining pleasant thoughts results in increased muscle activity in the cheek area responsible for smiling (the zygomatic muscle). A different set of muscles at the eyebrows – called corrugator muscles – are more active during the imagining of unpleasant thoughts (Schwartz, Brown and Ahern, 1980). Activity in the zygomatic muscles has also been found to increase when participants listen to stories with a sexual content rather than a nonsexual content but that corrugator activity is greater
when the stories were sexual and unpleasant (Sullivan and Brender, 1986).
Electrocardiography (ECG/EKG) Cardiac muscle activity is recorded in a similar way to that of skeletal muscle but the differences between the recordings are greater than the similarities. Electrocardiography (ECG) refers to the study of the electrical potentials generated by the working of the heart. Before understanding how biological psychologists measure heart activity, it’s useful to know a little about how the heart works. When the heart contracts, it produces an electrical current (as do all other muscular contractions). By placing electrodes near the source of the current, scientists can measure the electrical activity of the heart. The contraction of the heart is the consequence of the organ’s chief
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function – to pump blood around the body. The heart is made up of four chambers which pump blood to the body’s tissues. The two chambers at the top of the heart are the atria; the two at the bottom are the ventricles. The atria receive blood returned by the body’s veins; the ventricles pump blood away from the heart via arteries (a useful way of remembering the direction in which the blood goes is to think of arteries taking blood away). When you feel – or record – your heartbeat, you are feeling or recording the contraction of the heart as it pumps blood. It beats, on average, 72 times a minute (72 bpm or beats per minute) and, therefore, about 100,000 times a day. The contraction phase of the heart’s activity is called systole; the relaxation phase is called the diastole. The activity of the heart recorded by electrodes can be seen in a typical type of electrical wave. The wave is made up of various characteristic deflections (the direction of the wave characterises various points leading to and during the contraction) – these are the P, Q, R, S and T waves. The P wave is a small deflection produced by the current generated before contraction of the atria; the QRS complex of waves is produced by what is known as depolarisation (more on this later in the chapter) prior to the contraction of the ventricles. The R wave is the largest, most prominent wave. The T wave is the next, small blip-like, deflection after the large R wave and occurs as a result of activity in the ventricles. The P–Q interval lasts about 160 milliseconds; the Q–T interval lasts around 300 milliseconds. It takes around 370 milliseconds to go from the T wave to the next contraction. Figure 4.20 illustrates a typical ECG. In a study of cardiovascular activity and competitiveness, Harrison et al. (2001) asked male and female undergraduates to play a motor racing game either alone,
Figure 4.20 This is the PQRST complex of the ECG which represents a heartbeat. Each peak and trough of this complex represents some activity of the heart as it contracts and relaxes. Source: Daniel Sambraus/Science Photo Library Ltd.
in competition with the experimenter or in cooperation with the experimenter. The competitive condition was associated with significant increases in blood pressure and heart rate whereas the cooperative condition produced barely discernible changes in activity, a finding that echoes reports in the literature of reduced or stable cardiovascular activity in response to stress in the presence of a supportive person (what is known as social affiliation). Heart rate changes can be seen in response to a number of psychological variables. The promise of financial reward for persuading others (Smith et al., 1990), fear of needles (Shapiro, 1975) and playing Space Invaders (Turner et al., 1983) have all been found to increase heart rate.
Electrodermal response (EDR)/galvanic skin response (GSR) The measurement of electrical activity of the skin – electrodermal response (EDR) or galvanic skin response (GSR) – may seem to be completely irrelevant to the study of psychology. The technique, however, is surprisingly useful because skin conductance changes can be influenced by experience of positive and negative emotion, the degree of thinking that goes into the processing of information, and in perceptual awareness. In fact, a French neurologist, Charles Fere, was the first to note in 1888 that changes in a person’s mood and environment could lead to changes in the electrical activity recorded from the skin. The recording of electrodermal activity is based on the properties of skin and what skin does. Human skin has two layers – the epidermis, the outer layer which is about 1 mm thick, and the dermis, the inner layer which varies in thickness depending on the part of the body; it is thinner in the eyelids than the palms of the hands or soles of the feet, for example. The dermis contains blood vessels, hair follicles, sensory nerves and, importantly for EDR, the secretory part of sweat glands. It is sweat which allows conductance to occur on the skin. The body has two types of sweat glands – apocrine and eccrine. The larger of the two are the apocrine glands which are found in especially hirsute regions such as the armpits and genitals. Sweat is odourless and the odour we associate with it is the result of the reaction between sweat and bacteria on the skin. The eccrine glands are distributed widely and cover most of the skin, with some exceptions (such as lips, outer ear and glans penis, amongst others). Sweat glands are most numerous on the palms of the hands and soles of the feet with around one inch squared of skin having about 3,000 glands (Fowles, 1986). EDR recorded from fingers and palms responds more strongly to sensory stimulation than to physical stimuli such as heat; the opposite pattern is found for EDR recorded from the forehead, neck and back of the
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hands which dictates the position of electrodes in EDR recording. Skin conductance increases with increased stress, arousal and cognitive activity and reduces when the organism’s level of activity is low. During states of anxiety, for example, there is a great deal of sweating, especially in the palms. To show how the EDR measure can record changes in behaviour that are not immediately visible, some studies have reported increases in arousal to stimuli that are familiar. For example, Tranel et al. (1985) found that when students viewed slides of familiar and unfamiliar faces, skin conductance response was higher when they viewed the familiar faces (even when the participants themselves reported not having seen the face before; they had, in fact, viewed the faces in a previous slide show, which suggests that the body can reveal more than can self-reports). In an intriguing study, Tranel and Damasio (1985) measured skin conductance response in prosopagnosics (remember from an earlier section that these patients are unable to recognise familiar faces such as those of family members). They found that although the patients could not recognise familiar faces, galvanic skin response (GSR) would increase during the presentation of familiar faces, perhaps suggesting a degree of unconscious processing in these patients. Perhaps one of the more well-known, although poorly validated uses of GSR, is the polygraph, the so-called liedetector. While its ability to detect actual liars is abysmal, GSR has been found to be a very useful technique when measuring the responses of some criminals – specifically, psychopaths – to emotional stimuli. Psychopaths are people who are utterly remorseless, superficially charming,
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In Meet the Parents, Robert De Niro’s character makes good use of the polygraph to intimidate his son-in-law, played by Ben Stiller. Research, however, indicates that the polygraph is a poor measure of deception. Source: Universal/Everett/Rex Features.
manipulative and socially deviant. Jailed psychopaths have been found to show little GSR in response to emotional stimulation, a result that has also been found in studies of patients with damage to the front part of the brain (Raine, 1997). This is explored in the personality disorders section of Chapter 18.
Cutting edge – James Bond and the bloody consequences of Mortal Kombat participant, the less pronounced these changes were. When the protagonist was wounded or killed, there was a similar GSR increase but also an increase in two sets of facial muscles and a decrease in another set. These results suggest that the emotional consequences of attacking another or of being attacked can be characterised by subtle, facial muscle changes. Continuing this theme, blood (or its appearance) can also elicit strong psychophysiological reactions. Bartlett et al. (2008) asked 65 men to play the Mortal Kombat: Deadly Alliance game as their heart rate was measured. The game differed in the amount of blood that was present in the game – a lot, a moderate amount, a low amount or none. Men in the high and moderate quantity conditions showed the greatest amount of heart rate and also the greatest levels of hostility.
M
What man has not thought of spending a day in James Bond’s shoes (and what woman has not guffawed at the thought that this is what men would like to do)? A recent study has investigated people’s psychophysiological responses while they played James Bond in the game, JB007: Nightfire (Ravaja et al., 2008). In the experiment, GSR and EMG were recorded while people either killed or wounded ne’er-do-wells, or were wounded and killed themselves. The aim was to discover the psychophysiological responses generated by different emotional and moral perspectives. When an opponent was wounded or killed, participants’ skin conductance increased but some of the muscles in the face (zygomatic, orbicularis occuli and corrugator mucles, all found around the eyes and mouth) decreased. The more psychotic the
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Cutting edge – Continued Men in the low or no-blood condition did not produce these increases. Moreover, in the high/moderate condition, the
players were more likely to use their character’s weapon more often.
Playing at being James Bond. Putting yourself in the position of another, especially when this position is not normally encountered in real life, produces changes in physiology that are invisible to the human eye but can be recorded by psychophysiologists. Subtle and not-so-subtle cues in the environment – such as the presence of blood – can influence the degree to which we become aggressive. Men playing a game with blood visible show a faster heart rate and greater hostility than do those who saw no blood. Source: Alamy Images. Top Foto: Sony Pictures
Neuroimaging techniques The development of machines which can be used to investigate the brain’s structure and activity has revolutionised neuroscience. These sophisticated techniques, more than any of the others, have provided neuroscientists with the opportunity of measuring how the whole, living, healthy brain functions. They are called neuroimaging techniques because they allow us to visualise and obtain images of brain function and structure. These techniques include CT, MEG, PET, MRI and fMRI. PET and fMRI are measures of brain activity; CT and MRI are measures of brain structure. Figures 4.21 (a) and (b) show how studies using these techniques have increased during the period 1988 to 1998.
narrow beam of X-rays through a person’s head (see Figure 4.22(a)). The beam is moved around the patient’s head, and a computer calculates the amount of radiation that passes through it at various points along each angle. The result is a two-dimensional image of a ‘slice’ of the person’s head, parallel to the top of the skull. Using the CT scanner, an investigator can determine the approximate location of a brain lesion in a living patient. Knowing the results of behavioural testing and the location of the brain damage, the neuropsychologist can compare them and make inferences about the normal function of the damaged brain tissue. Figure 4.22(b) shows CT scans of the brain of a patient with a lesion caused by a stroke.
Magnetoencephalography (MEG) Computerised tomography (CT) Computerised tomography (CT) is a technique used to display the structure of the brain (tomos, meaning ‘cut’, describes the CT scanner’s ability to produce a picture that looks like a slice of the brain). The scanner sends a
A more recently developed electrophysiological technique is magnetoencephalography. Neurons can generate magnetic as well as electrical currents and these magnetic fields can be measured from the surface of the head via a machine called a superconducting quantum interference
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Figure 4.21 (a) The number of PET and fMRI studies of behaviour has increased significantly since 1988. Source: Cabeza, R. and Nyberg, L. Imaging cognition II: An empirical review of 275 PET and fMRI studies, 2. Journal of Cognitive Neuroscience, 2000, 12(1), 1–47. Reprinted by permission of the authors.
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Figure 4.21 (b) Shows the proportion of the methods used in abstracts submitted to the 2005 Annual Meeting of the Cognitive Neuroscience Society. F = functional imaging; E = electrophysiological; P = patient; B = behavioural; T = TMS; O = Other. Source: Chatterjee, A. A madness to the methods of cognitive neuroscience? Journal of Cognitive Neuroscience, 2005, 17, 6, 847–9, Figure 1. © by the Massachusetts Institute of Technology.
Figure 4.22 (b) A set of CT scans from a patient with a brain lesion caused by a stroke; left and right are traditionally reversed on CT scans, the brain lesion is actually in the right hemisphere. Source: Courtesy of Dr J. McA. Jones, Good Samaritan Hospital, Portland, Oregon, USA.
Figure 4.22 (a) A patient being placed in a computerised tomography (CT) scanner. Source: Hank Morgan/Rainbow. Reproduced with permission.
device (SQUID) which is immersed in liquid helium. The machine detects the activity of magnetic fields from a large number of neurons because the magnetic fields generated by single neurons are very weak. The subsequent recording is called the magnetoencephalograph or MEG. Unlike the EEG, MEG can be used to localise sources of activity fairly well and these sources can be plotted on a three-dimensional image of the participant’s head. MEG has been used to study various functions from language to olfaction.
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Positron Emission Tomography (PET) Positron emission tomography (PET) is an invasive measure of brain metabolism, glucose consumption and blood flow. The procedure for undergoing a PET scan goes something like this. A person is given a harmless dose of a radioactive substance (a form of glucose) which enters the brain (this is why the technique is invasive; the radioactive substance is injected into the participant’s arm). The chemical accumulates in particular regions of the brain (the location depends on the specific chemical) but usually goes to active cells. PET measures brain activity by examining the amount of oxygen consumed by, or blood flow travelling to, neurons. The radioactive parts of the glucose emit positrons (hence positron emission) which are detected by a PET scanner, a large, doughnut-shaped piece of equipment which accommodates the prostrate participant’s head. This activity is then represented in the form of coloured maps. Because of the radioactivity involved, only certain participants are allowed to take part in PET research. Premenopausal women and children, for example, cannot take part, which limits the use of PET when investigating how brain function develops during the early years. See Figure 4.23. It is difficult to overestimate the early contribution of PET research to the study of brain function, however. PET has allowed researchers to undertake investigations of the workings of the brain that were thought unrealisable 30 years ago. It is an expensive technique (the scanner’s costs run into millions) but a number of PET laboratories now
Figure 4.23 A PET scanner. Source: Corbis/Owen Franken
exist around the world and the results from these laboratories have allowed us to see whether the technique shows a consistent pattern of findings (Cabeza and Nyberg, 2000). In later chapters, you will see how PET research has helped us to understand the neural basis of functions such as speech perception, speech comprehension, memory, reading, attention and many others. It has been used to localise the parts of the brain active during word and speech recognition (Petersen et al., 1988; Zatorre et al., 1992; Castro-Caldas et al., 1998; Karbe et al., 1998), face perception (Sergent et al., 1992), language tasks performed by dyslexic individuals (Rumsey et al., 1997; Brunswick et al., 1999), problem-solving (Baker et al., 1996; Nagahama et al., 1996) and remembering events (Fletcher et al., 1998 a, b), among others.
Magnetic Resonance Imaging (MRI) and functional Magnetic Resonance Imaging (fMRI) A magnetic resonance imaging (MRI) scanner provides more detailed images of the structure of the brain than does CT (see Figure 4.24). It does so with the use of magnetic fields and radio waves rather than with X-rays. When a magnetic field is passed over the head, reverberations are produced by hydrogen molecules. These reverberations are picked up by the scanner which can convert the activity into a structural image. This image appears in a form like that seen in Figure 4.25.
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Figure 4.24 A colour-enhanced sagittal MRI scan. Source: Scott Camazine/Photo Researchers Inc.
It is also possible to use MRI in a functional capacity, to examine the brain’s function as well as its structure (Frackowiak et al., 1997). This is called functional magnetic resonance imaging (fMRI) and the technique is a measure of the amount of deoxygenated blood in parts of the brain (giving what is called the BOLD signal). The BOLD signals are converted into a form of pixel (in fMRI they are called voxels). Each image contains between 40,000 and 500,000 voxels and each voxel covers between 1 and 123 mm3 of brain tissue (Vul et al., 2009). Unlike PET, which is invasive (radioactively labelled substances are introduced into the body), MRI and functional MRI are non-invasive, which means that they can be used to investigate the development of function (in, for example, children). fMRI has been used to investigate similar functions to those investigated using PET: language, attention, vision, memory and so on. Both PET and MRI can be used in combination. However, while both have the advantage of good spatial resolution (you can see images and structures more precisely), they also have the disadvantage of poor temporal resolution – it is difficult to match the psychological and neural event in time precisely. The reason for this is that in PET and fMRI a number of scans are recorded and then averaged (see Caveats below).
Figure 4.25 An MRI scan taken from a patient with damage to Wernicke’s area, following a stroke (the right side of the image represents the left side of the brain). Source: Figure 4.27 from Human Neuropsychology, 2nd edn, p. 36, Pearson/Prentice Hall (Martin, G.N., 2006).
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Functional MRI has been used to understand the cerebral correlates of a variety of topics, from being in love (Bartels and Zeki, 2000), to naming animate and inanimate objects (Martin and Chao, 2001), to driving (Horikawa et al.,
2005), to navigating a virtual London (Spiers and Maguire, 2007), to friendship and the understanding of magic. The last two in this list form the two Cutting Edge sections.
Cutting edge – Love, friendship and neuroscience Researchers from the US and Switzerland used fMRI to see how quickly people would respond to words when the name of a loved one, a friend or a ‘passionate hobby’ (e.g. dance) was subliminally presented before the words (Ortigue et al., 2007). When the word was preceded by a loved one’s name or a favoured hobby, reaction time was faster – and activation was greater in areas near the frontal lobe, called the fusiform gyrus and angular gyri. The results suggest that a photograph of a loved one acts as a motivating prime but that it activates a network of brain regions not normally associated with reward. This motivated attention is also seen in ERP studies. Psychologists from the Netherlands used event-related potentials to see whether stimuli related to a loved one would elicit a late, positive-going brainwave normally found when people are exposed to emotional stimuli (Langeslag et al., 2007). This is what they found – the wave was larger to the face of a loved one than to a friend or that of an unknown, beautiful person. Friendship, of course, is one aspect of love. In another study, also from researchers in the Netherlands, participants were asked to approach or withdraw from photographs of faces of liked and disliked peers, friends and familiar celebrities, as
fMRI measured brain activation (Guroglu et al., 2008). In the task, a face was presented on screen and, using a joystick, participants moved a stimulus on screen towards instructions that read ‘I want to approach’, ‘neutral’ and ‘I want to go away’. Liked stimuli were approached more than disliked ones and peers more than celebrities. During interaction with friends, four regions were especially activated (the amygdala, hippocampus, nucleus accumbens and ventromedial prefrontal cortex; see below), regions known to be implicated in empathy. Two of these regions were also activated in a study from the UK and US where people played a videogame in which they either (i) shot an aggressive humanoid or healed a passive, wounded person or (ii) shot the wounded and helped the assailant (King et al., 2006). The aim was to discover the neural substrates of compassionate and violent behaviour, or ‘doing the right thing’. Activation was found in the amygdala and the ventromedial prefrontal cortex regardless of whether the participants helped the wounded or attacked an assailant, suggesting that both regions are implicated in our ability to ‘do the right thing’ and our understanding of what it is to behave appropriately.
Cutting edge – The magic of neuroimaging or ‘You’ll like this, not a lot, but you’ll like this’ How do we and our brains cope with a violation of what we consider to be normal? Psychologists from the Universities of Durham and Exeter used fMRI to measure how the brain responded to these violations (Parris et al., 2009). A group of young men and women watched video clips of various elementary magic tricks – such as the disappearing coin, where the magician leaves a coin on the table, covers it, and lifts the cover to reveal it has disappeared; a levitation trick where a paper cup is made to levitate, and a cigarette torn and then restored to its intact state. They also watched clips of sequences that were similar but which did not violate expectations.
When they saw the the magic trick, there was significant activation in a part of the frontal lobe, called the dorsolateral prefrontal cortex, and a nearby area, the anterior cingulate cortex. Activity was also greater here than when a person watched a clip of something that was surprising – activity seemed to be dependent on the unfathomable nature of the trick rather than on its surprise value. (See Figure 4.26). The unusual study highlights a part of the brain that may be involved in the understanding of causal relations in what we perceive. Chapter 11 has more on the role of this region during reasoning.
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Cutting edge – Continued
Figure 4.26 Changes in various parts of the frontal lobe as people watch a magic trick. Source: Parris, B.A., Kuhn, G., Mizon, G.A., Benattayallah, A. and Hodgson, T.L. (2009). Imaging the impossible: An fMRI study of impossible causal relationships in magic tricks. Neuroimage, 45, 1033–39.
Caveats Of course, neuroimaging techniques, although providing us with a new way of viewing brain activation, are not measures of actual neural functioning. Instead, they measure the processes associated with neural function – such as blood flow or oxygen and glucose consumption. They also provide data that are correlational. Researchers draw associations between the stimulus or task they present and the differences in activation in the brain they observe that are not seen at baseline. These data are not particularly time-sensitive because fMRI and PET use the technique of averaging and subtraction – several experimental scans are taken, usually in a mixed order, and then averaged to produce a scan for this condition/group. A scan is taken approximately every three seconds. The average experimental condition is subtracted from the control scan. This means that you cannot associate a scan with a specific event in time. Also, because any task will activate all of the brain to some extent, researchers focus on a region of interest (ROI) and compare activation between two tasks in this area. These scans are also very persuasive tools. Examine any newspaper report involving the brain and the chances are
that the story either involves some new ground-breaking drug or neuroimaging (see the opening vignette for an example). The appeal of neuroimaging is seductive. It is immediate, visual and allows us to see something that was previously unattainable: a pictorial, anatomically correct representation of the living brain. And, as humans, we are very swayed by visual seduction, as McCabe and Castel (2008) have demonstrated in their study. They asked people to judge the degree of scientific reasoning in three articles about cognitive neuroscience. The articles were accompanied by either bar graphs, topographical maps (brain scans) or no image. Despite there being no difference between the content of the articles, the piece accompanied by a brain map was judged to be more scientific. These images, say McCabe and Castel, ‘provide a physical basis for abstract cognitive processes, appealing to people’s affinity for reductionistic explanations for cognitive phenomena’ (p. 343). Neuroimaging is being applied to some novel areas of behaviour. A new line of research has examined a particularly controversial topic: the use of neuroimaging to predict lying. The evidence is reviewed in the Controversies in Psychological Science section.
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Controversies in Psychological Science – Can brain scanners detect deception? The issue If all it took to identify a liar was to examine their extending, Pinnochio-like proboscis, we would encounter a lot less deception and the police and the courts could probably take a day off. But we do not yet have a Pinnochian ‘tell’ that can do this (you read about the evidence in Chapter 1). Some scientists, however, have tried to identify one. And, controversially, it involves the brain.
The evidence Psychology has a long history of using physiological measures to identify deception. The polygraph, described in the section earlier, is one measure. This has its critics – it has rightly been taken to task for being methodologically questionable (the polygraph is a measure of arousal, rather than deception). The key to identifying a neurophysiological marker of deception is attractive to those who could exploit it. This tell-tale activation may not be under conscious control – the liar may not be able to control their brain activation – and it may be present only when a person is lying. It is almost like using neuroimaging as a mind-reading tool, where the observation of a scan would reveal your innermost thoughts and predict your thinking and behaviour. This, however, is currently pie in the sky – the Eternal Sunshine of the Spotless Mind is a long way off, if possible at all – but psychologists and neuroscientists have worked at constructing ways in which the brain’s behaviour can be measured during acts of deception (Langleben, 2008; Spence, 2008; Sip, Roepstorff, McGregor and Frith, 2007). According to Vrij (2004a, b), deception involves ‘a deliberate attempt, without forewarning, to create in another a belief which the communicator considers to be untrue’. This definition embodies two important points: (i) a liar deliberately and purposefully intends to deceive another person and (ii) deception does not involve instructing the liar to lie – he or she will do this spontaneously. Around 16 peer-reviewed studies using fMRI to study deception had been published by 2007 (Spence, 2008). Almost all of these studies have implicated one particular part of the brain in deception – the frontal lobes. The majority of the reports specifically find activation in certain areas of the frontal lobes: the ventromedial prefrontal cortex (VPC), dorsolateral prefrontal cortex (DFC) and the anterior cingulate cortex (ACC). For example, researchers have asked participants to lie to the experimenter (Abe et al., 2007). or given them two cards and asked them to lie about having one of them (Gamer et al., 2007) or asked volunteers to malinger – feign a memory impairment (Lee et al., 2002; 2005), or instructed them to ‘steal’ a watch or ring and then reward them for successfully lying about it (Kozel
Headlines such as these are becoming more common (but no more accurate) Source: Guardian News and Media Ltd.: Charles O’Rear/Corbis
et al., 2005), or asked them to lie about autobiographical events (Spence et al., 2001; Nunez et al., 2005). All activated the prefrontal cortex and some activated the medial temporal gyrus. These activations were not observed when the person was telling the truth or when baseline recordings were taken. According to Spence et al. (2008), the VPC may support deceptive behaviour by suppressing a person’s ability to tell the truth. It seems that deception can, therefore, be measured by fMRI. Or can it? According to Sip et al. (2007), fMRI studies of deception are hamstrung by several methodological problems or confounds. They argue that what deception experiments primarily measure are the functions needed for lying, such as inhibiting behaviour (telling the truth), mentalising (reading others’ states of mind or intentions) and relating action or behaviour to the outcome (monitoring behaviour). The authors suggest that deception involves keeping track of the lies and truth being told (information management), building trust with the deceived (impression management), appreciating that the gains from lying are greater than the losses and the risks of being found out (risk management) and an intention that lying is done for some good or can be justified in some way (reputation management). All of these behaviours recruit the areas found to be active during deception. See Figure 4.27.
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Figure 4.27 Some of the areas of the brain, principally involving the frontal lobe, which become active during the act of lying. Source: Spence, S.A., Kaylor-Hughes, C., Farrow, T.F.D. and Wilkinson, I.D. (2008). Neuroimage, 40, 1411–18.
The problem, however, is that in all fMRI experiments, the participants are instructed to lie by the experimenter. That is, they do not spontaneously lie and, furthermore, do not lie about anything significant (lying about having a playing card is in a different order to lying about running someone over in a car). These participants lack one of the key features of deception – the intention to lie, although it is possible that a person can be instructed to lie on someone’s behalf (i.e. provide a false alibi for a criminal). But, then again, the person is motivated to do this – it has a purpose. The protocols used also neglect the context in which lying occurs and the negative consequences of lying – a person who lies faces no punishment or no censure at all in these experiments. Again, the paradigms used can be regarded as basic and artificial. Because of these problems, Sip et al. have identified a number of related problems in the interpretation of fMRI studies. The first is that although a characteristic of mentalising, emotion and risk-taking is activation in a particular part of the brain, the presence of such activation does not mean that a person is lying. The second is that fMRI deception
Modern brain stimulation: transcranial magnetic stimulation (TMS) Despite having its origins in the nineteenth century, a relatively new, non-invasive, technique for studying localisation is transcranial magnetic stimulation (TMS). TMS involves modulating cortical activity by passing alternating magnetic fields across the scalp (Burt et al., 2002). The consequence of exposure to these fields is that electrical currents are induced in the cortex and the excitability of the cortex is subsequently increased or decreased. These effects can last a few seconds or minutes to a few weeks. The technique’s benefits to neuropsychol-
studies are based on groups – individual responses may vary greatly (depending on the seriousness of the wrongdoing and the individual’s predisposition to lie or intention to lie). A third is that instructions to lie ‘lift moral sanctions against lying’ – there are no real consequences of lying. The fourth is that different people will have different attitudes to deception. At the extreme, think of the psychopath (described in detail in Chapter 18). A psychopath lies effortlessly and shows no empathy – he (and it is usually a he) shows reduced frontal lobe volume and activation, not more. Psychopaths’ behaviour stems from their attitude to their victim – they do not regard what they say as wrong when they lie.
Conclusion In the US, some scientists, entrepreneurs and patent specialists are busying themselves setting up and protecting companies that they claim will use fMRI to detect deception (for example, NoLieMRI in San Diego). However, what the studies to date have done is not so much measure deception but the cognitive processes involved in deception. Importantly, these studies have a flaw – the liar does not spontaneously lie or has the intention of lying, unlike genuine deception. Future studies, therefore, need a way of allowing a person to decide whether to lie. Of course, these studies will be so tightly straightjacketed that another important element will still be missing – the belief that lying will spare some punishment or will achieve some other, very significant goal. As Sip et al. conclude, ‘paradigms are still inadequate. The problems that bedevilled old techniques have not been eliminated by the new’. It seems as if there is still no room for Pinnochio’s nose inside the scanner.
ogy are that it can produce transient impairment or improvements in cognition non-invasively. In practice, a metal coil is placed on a participant’s scalp, as you can see in Figure 4.28. The alternating electrical current in the coil produces an alternating magnetic field at right angles to the current generated in the coil. This alternating magnetic field then passes through to the cortex and creates an electrical current in the part of the brain (around 1 to 2 cms worth) beneath the coil. The technique is apparently safe – the most likely danger, if a danger occurs, is of a seizure being generated during repeated stimulation. Sometimes headaches can follow and slight periods of mania; scalp facial muscles might twitch.
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Figure 4.28 A typical rTMS procedure. Source: University of Durham/Simon Fraser/Science Photo Library Ltd.
In TMS, the magnetic fields – or ‘pulses’ – can be presented either singly, in pairs a few seconds apart or in quick succession over a period of minutes. These are called single-pulse TMS, paired-pulse TMS and repetitive (r)TMS, respectively. Testing sessions normally last between 20 minutes and an hour. If the stimulation is high frequency, an increase in blood flow is observed; if stimulation is low, excitability is reduced (Chen et al., 1997). Blood flow and cortical excitability are thought to be correlates in this sense although the change in blood flow may occur away from the region that is cortically excited. The effect of TMS in normal, healthy individuals is analogous to the effect of a lesion – the transient stimulation
produces a transient brain disruption of function (although, obviously, with no damage, permanent or otherwise). Unlike neuroimaging, where activation is correlated with behaviour and may not be necessary to produce it, TMS directly stimulates brain regions and the consequences can be observed. The technique has been found to disrupt verbal working memory (Mottaghy et al., 2002), verb generation (Shapiro et al., 2001) and speech (Stewart et al., 2001). Other studies have reported improvements in picture naming following TMS stimulation of Wernicke’s area (Topper et al., 1998). Repetitive TMS has been used in a very novel way. Fregni et al. (2008) used it to stimulate a part of the front
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region of the brain – the dorsolateral prefrontal cortex (DPFC) – while participants were exposed to foods such as chocolate cake, toast and sweets, or a film of foods that strongly induced craving. Participants rated how much they desired food before and after stimulation. Right-sided stimulation reduced craving after watching food whereas stimulation of the left side reduced the time that participants fixated on the food. Stimulation on both sides of the brain reduced the amount of food that people ate afterwards, compared to a sham condition (in which participants thought they were receiving brain stimulation but did not). This part of the brain is associated with cravings for other types of substances – such as nicotine. Smokers watching a video involving smoking showed increased activation in several brain regions, including the prefrontal cortex (McBride et al., 2006) and stimulating the right DPFC reduces risk-taking behaviour (Knoch et al., 2006). Perhaps, the authors suggest, modulating activity in this part of the brain inhibits neural circuits involved in reward.
Control of behaviour The brain has two roles: controlling the movements of the muscles and regulating the physiological functions of the body. The first role looks outwards towards the environment and the second looks inwards. The outwardlooking role includes several functions: perceiving events in the environment, learning about them, making plans, and acting. The inward-looking role requires the brain to measure and regulate internal characteristics such as body temperature, blood pressure and nutrient levels.
tion from the body senses. Different regions of the primary somatosensory cortex receive information from different regions of the body. In addition, the base of the somatosensory cortex receives information concerning taste. See Figure 4.29.
Primary sensory and motor cortex The three regions of primary sensory cortex in each hemisphere receive information from the opposite side of the body. Thus, the primary somatosensory cortex of the left hemisphere learns what the right hand is holding, the left primary visual cortex learns what is happening towards the person’s right, and so on. The connections between the sensory organs and the cerebral cortex are said to be contralateral (contra ‘opposite’, lateral ‘side’). The region of the cerebral cortex most directly involved in the control of movement is the primary motor cortex (MI), located just in front of the primary somatosensory cortex. Neurons in different parts of the primary motor cortex are connected to muscles in different parts of the body. The connections, like those of the sensory regions of the cerebral cortex, are contralateral; the left primary motor cortex controls the right side of the body and vice versa. Thus, for example, damage to the left primary motor cortex will result in paralysis in
Primary visual cortex (mostly hidden from view) Primary auditory cortex (mostly hidden from view)
Primary motor cortex
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Organisation of the cerebral cortex We become aware of events in our environment e by means of the five major senses: vision, audiyp tion, olfaction (smell), gustation (taste) and the sych somatosenses (‘body’ senses: touch, pain and temperature). Three areas of the cerebral cortex receive information from the sensory organs. The primary visual cortex (V1), which receives visual information, is located at the back of the brain, on the inner surfaces of the cerebral hemispheres. The primary auditory cortex, which receives auditory information, is located on the inner surface of a deep fissure in the side of the brain. The primary somatosensory cortex, a vertical strip near the middle of the cerebral hemispheres, receives informan myp
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Figure 4.29 The lobes of the brain and the association areas of the cortex, together with the primary functions undertaken by these areas.
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the contralateral hand and sometimes in the left hand (Haaland and Harrington, 1989). The hand that one predominantly uses (and this usually means to write with) appears to be related to the side of the brain that is involved in speech production (we’ll discuss handedness more in Chapter 10).
Association cortex The regions of primary sensory and motor cortex occupy only a small part of the cerebral cortex. The rest of the cerebral cortex accomplishes what is done between sensation and action: perceiving, learning and remembering, planning, and acting. These processes take place in the association areas of the cerebral cortex. The central fissure provides an important dividing line between the anterior (front) part of the cerebral cortex and the posterior (back) regions. The anterior region is involved in movement-related activities, such as planning and executing behaviours. The posterior part is involved in perceiving and learning. The cerebral cortex is divided into four areas, or lobes, named after the bones of the skull that cover them: the frontal lobe, parietal lobe, temporal lobe and occipital lobe. The brain contains two of each lobe, one in each hemisphere. The frontal lobe (the ‘front’) includes everything in front of the central fissure. The parietal lobe (the ‘wall’) is located on the side of the cerebral hemisphere, just behind the central fissure, behind the frontal lobe. The temporal lobe (the ‘temple’) juts forward from the base of the brain, beneath the frontal and parietal lobes. The occipital lobe (ob ‘in back of’, caput ‘head’) lies at the very back of the brain, behind the parietal and temporal lobes. The lobes and association regions of the brain can be seen in Figure 4.30 (a) and an overview of the brain’s motor functions can be seen in Figure 4.30 (b).
Temporal sequencing of events Each primary sensory area of the cerebral cortex sends information to adjacent regions, called the sensory association cortex. Circuits of neurons in the sensory association cortex analyse the information received from the primary sensory cortex; perception takes place there, and memories are stored there. The regions of the sensory association cortex located closest to the primary sensory areas receive information from only one sensory system. For example, the region closest to the primary visual cortex analyses visual information and stores visual memories. Regions of the sensory association cortex located
far from the primary sensory areas receive information from more than one sensory system; thus, they are involved in several kinds of perception and memory. These regions make it possible to integrate information from more than one sensory system. For example, we can learn the connection between the sight of a particular face and the sound of a particular voice. Just as regions of the sensory association cortex of the posterior part of the brain are involved in perceiving and remembering, the frontal association cortex is involved in the planning and execution of movements. The anterior part of the frontal lobe – known as the prefrontal cortex – contains the motor association cortex. The motor association cortex controls the primary motor cortex; thus, it directly controls behaviour. Obviously, we behave in response to events happening in the world around us. Therefore, the sensory association cortex of the posterior part of the brain sends information about the environment to the motor association cortex (prefrontal cortex), which translates the information into plans and actions (see Figure 4.30).
Lateralisation of function Although the two cerebral hemispheres cooperate with each other, they do not perform identical functions. Some functions show evidence of lateralisation, that is, they are located primarily on one side of the brain (this is also called functional hemispheric asymmetry). It is commonly suggested that the left hemisphere participates in the analysis of information (making it good at recognising series of events) whereas the right hemisphere is good at putting items together (making it good at ‘holistic’ activities). This distinction may, however, be too simplistic. The left hemisphere does appear to be significantly more involved in aspects of language processing such as speech production and comprehension and the appreciation of the sounds in speech than is the right hemisphere. However, as you will see in more detail in Chapter 10 (Language), the right hemisphere is better than the left hemisphere at comprehending metaphors and may undertake the linguistic duties of the left hemisphere when the left is damaged. The right hemisphere also appears to be superior to the left at recognising faces, perceiving emotion and mentally rotating three-dimensional images in space. In the following chapters you will read about these and other examples of function that are lateralised in the brain; you will see that lateralisation of function does not occur in the whole of one hemisphere but in specific parts of it.
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Motor association cortex (prefrontal cortex) Primary auditory cortex (mostly on inner surface)
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Figure 4.30 (a) The relation between the association cortex and the regions of primary sensory and motor cortex. Arrows refer to the flow of information. (b) A motor homunculus. This shows how some parts of the brain are disproportionately involved in certain bodily movements, such as those involving the lips and hands. This little figure illustrates the relative amount of cortex devoted to each body part’s movement. Source: Carlson, N.R., Physiology of Behavior (6th edn), p. 235. Boston: Allyn & Bacon, 1988. © Allyn & Bacon. Reproduced with permission.
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The two cerebral hemispheres are connected by the corpus callosum, a large band of axons, seen in Figures 4.31 (a) and (b). In fact, it is the brain’s largest collection of connective fibre. The corpus callosum connects corresponding parts of the left and right hemispheres: the left and right temporal lobes are connected, the left and right parietal lobes are connected, and so on. Because of the corpus callosum, each region of the association cortex
knows what is happening in the corresponding region of the opposite side of the brain. Some people have the corpus callosum surgically cut in order to alleviate the symptoms of epilepsy. So-called split-brain patients are interesting to psychologists because their two hemispheres do not appear to be able to communicate. We discuss the effects of split-brain surgery in more detail in Chapter 9 (Consciousness).
Vision: the occipital lobe Inner surface of right cerebral hemisphere
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Pituitary gland Cerebellum Pons Medulla Spinal cord
The primary business of the occipital lobe – and the lower part of the temporal lobe – is seeing. Total damage to the primary visual cortex, located in the inner surface of the posterior occipital lobe, produces cortical blindness (to distinguish it from other forms of blindness such as congenital blindness). Because the visual field is ‘mapped’ onto the surface of the primary visual cortex, a small lesion in the primary visual cortex produces a ‘hole’ in a specific part of the field of vision. The visual association cortex is located in the rest of the occipital lobe and in the lower portion of the temporal lobe. Damage to the visual association cortex will not cause blindness. In fact, visual acuity may be very good; the person may be able to see small objects and may even be able to read. However, the person will not be able to recognise objects by sight. For example, when looking at a drawing of a clock, the person may say that they see a circle, two short lines forming an angle in the centre of a circle, and some dots spaced along the inside of the circle, but will not be able to recognise what the picture shows. On the other hand, if the person is handed a real clock, they will immediately recognise it by touch. This fact tells us that the person has not simply forgotten what clocks are. Similarly, the person may fail to recognise their spouse by sight but will be able to do so from the sound of the spouse’s voice. This deficit in visual perception is called visual agnosia (a- ‘without’, gnosis ‘knowledge’) and we return to it in Chapter 6 (Perception).
Audition: the temporal lobe
Figure 4.31 (a) A view of the brain that has been sliced through the midline (this is called a sagittal view). The corpus callosum unites the cerebral cortex of the two hemispheres. (b) A crosssection of a human head. You can clearly see the general structures of the brain: the neocortex, the corpus callosum, the cerebellum, the pons and the medulla. Source: (b) Image P330/382 Tissuepix/Science Photo Library Ltd.
The temporal lobe contains both the primary auditory cortex and the auditory association cortex. The primary auditory cortex is hidden from view on the inner surface of the upper temporal lobe. The auditory association cortex is located on the lateral surface of the upper temporal lobe. Damage to the primary auditory cortex leads to hearing losses, while damage to the auditory association cortex produces more complex deficits. Damage to the left auditory association cortex causes severe language deficits. People with such damage are no longer able to
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comprehend speech, presumably because they have lost the circuits of neurons that decode speech sounds. However, the deficit is more severe than that. They also lose the ability to produce meaningful speech; their speech becomes a jumble of words. Language deficits produced by brain damage are described in more detail in Chapter 10 (Language). See Figure 4.32. Damage to the right auditory association cortex does not seriously affect speech perception or production, but it does affect the ability to recognise non-speech sounds, including patterns of tones and rhythms. The damage can also impair the ability to perceive the location of sounds in the environment. As we will see later, the right hemisphere is important in the perception of space. The contribution of the right temporal lobe to this function is to participate in perceiving the placement of sounds.
Somatosensation and spatial perception: the parietal lobe The primary sensory function of the parietal lobe is perception of the body. However, the association cortex of the parietal lobe is involved in much more than somatosensation. Damage to a particular region of the association cortex of the left parietal lobe can disrupt the ability to read or write without causing serious impairment in the ability to talk and understand the speech of other people. Damage to another part of the parietal lobe impairs a person’s ability to draw. When the left parietal lobe is damaged, the primary deficit seems to be in the person’s ability
Primary motor cortex
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to make precise hand movements; their drawing looks shaky and sloppy. In contrast, the primary deficit produced by damage to the right parietal lobe is perceptual. The person can analyse a picture into its parts but has trouble integrating these parts into a consistent whole. Thus, they have difficulty drawing a coherent picture. We will look at disorders such as these in Chapter 6 (Perception). Most neuropsychologists believe that the left parietal lobe plays an important role in our ability to keep track of the location of the moving parts of our own body, whereas the right parietal lobe helps us to keep track of the space around us. People with right parietal lobe damage usually have difficulty with spatial tasks, such as reading a map. People with left parietal lobe damage usually have difficulty identifying parts of their own bodies by name. For example, when asked to point to their elbows, they may actually point to their shoulders. There is also evidence showing that this region of the brain, together with the frontal lobe, is involved in our ability to perform mental arithmetic (Menon et al., 2000; Cowell et al., 2000). This region is smaller in children with mathematical deficits when compared with children with normal maths performance (Isaacs et al., 2001). The posterior part of the parietal cortex (PPC) appears to be specialised for storing representations of motor actions (Milner, 1998). Snyder et al. (1997) found that some neurons in the PPC of two adult macaque monkeys were active before and during visually guided arm movements whereas others were active during eye movements. However, rather than directing attention to objects in space, the PPC seems to be responsible for the intention
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Figure 4.32 Broca’s area, located just in front of the face region of the primary motor cortex. This region is involved in the control of speech.
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to move. There may be visual neurons in the PPC which are responsible for visually guided movement (Sakata, 1997). Manipulation of body part information appears to involve the left frontal and parietal lobes whereas manipulation of numbers appears to involve the right parietal lobe (Le Clec’H et al., 2000). Neurons in a part of the brain called the superior temporal sulcus become active when an animal detects head and body movement. In humans, a similar area on the right side of the brain becomes activated when watching the movement of living things – whether in films, or of animals or schematic versions of human beings. One particular area, the extrastriate body area (EBA) seen in Figure 4.32 appears to become active selectively to the sight of human bodies and body parts and is also activated when we imitate the body actions of others (Jackson et al., 2006). Does this region integrate information from a moving human image and process the dynamic elements of human movement, or does it simply process static images? Researchers from the University of Bangor in North Wales used fMRI to measure brain activation while people watched single frames presented in the correct order from one whole body action (e.g. punching, kicking) or a series of frames involving several actions that were unrelated (Downing et al., 2006). They found that the EBA responded more strongly to the second set of images than the first, suggesting that this region may not be responsible for the representation of dynamic movement/biological motion but, instead, is involved in processing static images of movement.
Planning and moving: the frontal lobe Because it contains the motor cortex, the principal function of the frontal lobe is to mediate motor activity (it also includes the area responsible for speech perception, Broca’s area, seen in Figure 4.32). There is also evidence that the premotor area of the frontal lobes (and a part of the parietal lobe) contains mirror neurons (Rizzolatti et al., 1988). Mirror neurons are those which fire when we watch someone perform an action and also fire when we execute that action; they seem to mirror the activity of neurons that are involved in ‘doing’. For example, neurons in one part of this area are activated in monkeys when they make a grasping movement with their hand. However, a different set in the same region is also activated when the monkey sees another making reaching movements (Ferrari et al., 2003). Some people have associated dysfunction in these mirror neurons with autism, and the evidence for this is considered in Chapter 12. The frontal lobes are involved in a variety of ‘higher’ functions including planning, changing strategies, being
aware of oneself, empathising with others, evaluating emotional stimuli, inhibiting inappropriate behaviour and behaving spontaneously (some of these are called executive functions). Damage to the primary motor cortex produces a very specific effect: paralysis of the side of the body opposite to the brain damage. If a portion of the region is damaged, then only the corresponding parts of the body will be paralysed (Passingham, 1995). However, damage to the prefrontal cortex produces more complex behavioural deficits. For example, the person with frontal lobe damage will react to events in the environment but show deficits in initiating behaviour. When a person with damage to the prefrontal cortex is asked to say or write as many words as possible or is asked to describe as many uses for an object as possible, they will have great difficulty in coming up with more than a few, even though they have no problem understanding words or identifying objects by name (Eslinger and Grattan, 1993). People with damage to the frontal lobe also tend to have difficulty changing strategies. If given a task to solve, they may solve it readily. However, if the problem is changed, they will fail to abandon the old strategy and learn a new one. The Wisconsin Card Sorting Task, for example, presents patients with packs of cards on which are printed symbols of different shape, colour or number (see page 474, Chapter 11). The experimenter decides on a sorting criterion (shape, for example) and the patient has to detect which criterion it is by sorting the cards into piles, receiving feedback from the experimenter. When the criterion unexpectedly shifts, some patients are unable to detect this shift and carry on responding as if the previous criterion still applied. This is called perseveration. However, not all frontal lobe patients will exhibit this behaviour (Anderson et al., 1991), only those with damage to a specific region of the frontal lobe. People with damage to certain areas of the frontal lobe often have rather bland personalities. They seem indifferent to events that would normally be expected to affect them emotionally (Stuss et al., 1992). For example, they may show no signs of distress at the death of a close relative and do not show the typical physiological response to stress (see Martin 2006 for a comprehensive description). They have little insight into their own problems and are uncritical of their performance on various tasks (Stuss et al., 1992; Brazzelli et al., 1994; Hornak et al., 1996; Cicerone and Tanenbaum, 1997). The most famous case study of frontal lobe damage resulting in shifts in emotional and social behaviour is that of Phineas Gage, a man you read about in Chapter 1 and to whom we return in Chapter 13. In terms of daily living, the most important consequences of damage to the frontal lobe are probably lack of foresight and difficulty in planning. A person with
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injury to part of the frontal lobe might perform fairly well on tests of intelligence but be unable to hold down a job or organise their day (Eslinger and Damasio, 1985; Wood and Rutterford, 2004). Sequencing – the organisation of material in logical, correct or learned order – is grossly impaired in frontal patients (Sirigu et al., 1995). Often, when given tasks that tap everyday activities (such as undertaking an errand or following a recipe), patients with frontal lobe damage perform poorly (Shallice and Burgess, 1991; Fortin et al., 2003) and may engage in obsessive collecting behaviour (Anderson et al., 2005). Patients with damage to different regions of the frontal lobe exhibit different symptoms. For example, patients with damage to the orbitofrontal cortex (the tip of the frontal lobes) tend to exhibit impairments in social behaviour, personality and emotional expression but have relatively intact intellect. They are impulsive and don’t care what others think or feel. Eslinger and Damasio’s (1985) patient, EVR, is a good example. EVR, an ex-accountant who had a tumour removed from the same part of the brain injured in Phineas Gage, has superior intellect but an impaired ability to plan and organise his daily life. He performs at normal levels on tests such as the Wisconsin Card Sorting Task and he has superior IQ. However, his ability to maintain close relationships and a job and his ability to plan and organise his life are grossly impaired. Chapter 13 looks at EVR’s case in greater depth.
Control of internal functions and automatic behaviour The cortex consists of only the outer 3 mm of the surface of the cerebral hemispheres. There are other structures such as the brain stem, the cerebellum and the interior of the cerebral hemispheres which are important to the regulation of behaviour. The cerebellum helps the cerebral hemispheres to control movement and to initiate some automatic movements, such as postural adjustment, on its own. The brain stem and much of the interior of the cerebral hemispheres are involved in homeostasis and control of species-typical behaviours. Homeostasis (from the root words homoios ‘similar’, and stasis ‘standstill’) refers to maintaining a proper balance of physiological variables such as temperature, concentration of fluids, and the amount of nutrients stored within the body. Speciestypical behaviours are the more-or-less automatic behaviours exhibited by most members of a species that are important to survival, such as eating, drinking, fighting, courting, mating and caring for offspring.
The brain stem The brain stem contains three structures: the medulla, the pons and the midbrain. Figure 4.33 shows a view of the left side of the brain. The brain has been rotated slightly so that we can see some of the front of the brain stem, and the cerebral hemispheres are shown lightly so that the details of the brain stem can be seen. We also see the thalamus, the hypothalamus and the pituitary gland. The brain stem contains circuits of neurons that control functions vital to the survival of the organism in particular and of the species in general. For example, circuits of neurons in the medulla, the part of the brain stem closest to the spinal cord, control heart rate, blood pressure, rate of respiration, and – especially in simpler animals – crawling or swimming motions. Circuits of neurons in the pons, the part of the brain just above the medulla, control some of the stages of sleep, and circuits of neurons in the midbrain control movements used in fighting and sexual behaviour and decrease sensitivity to pain while engaged in these activities.
The cerebellum The cerebellum plays an important role in the control of movement. It receives sensory information, especially about the position of body parts, so it knows what the parts of the body are doing. It also receives information from the cortex of the frontal lobes, so it knows what
TOP Cerebral hemisphere
Thalamus
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Hypothalamus Pituitary gland Brain Stem
Midbrain Pons
Cerebellum Spinal cord
Medulla
Figure 4.33 The divisions of the brain stem: the medulla, the pons and the midbrain. The thalamus, hypothalamus and pituitary gland are attached to the end of the brain stem.
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movements the frontal lobes intend to accomplish. The cerebellum is basically a computer that compares the location of the body parts with the intended movements and assists the frontal lobes in executing these movements. Without the cerebellum, the frontal lobes would produce jerky, uncoordinated, inaccurate movements – which is exactly what happens when a person’s cerebellum is damaged. Besides helping the frontal lobes to accomplish their tasks, the cerebellum monitors information regarding posture and balance, to keep us from falling down when we stand or walk, and produces eye movements that compensate for changes in the position of the head. Some studies have suggested that the cerebellum may also be involved in a variety of other functions such as cognition and language (Schmahmann and Sherman, 1998). The ability to produce words fluently and to solve problems are impaired in patients whose cerebellum has been damaged (Grafman et al., 1992; Appollonio et al., 1993). Neuroimaging studies show that various parts of the cerebellum become active during tasks involving movement and touch, language and verbal memory, spatial memory, executive function and emotional processing (Stoodley and Schmahmann, 2009). Language has been associated with activation on the right and spatial awareness with the left, which is opposite to that pattern seen at the cortical level presumably because projections to it are crossed. Some psychologists have also implicated the cerebellum in the reading disorder, developmental dyslexia, (see Chapter 10, page 417).
Subcortical structures The thalamus If you stripped away the cerebral cortex and the white matter that lies under it, you would find a collection of brain structures. These are called subcortical brain structures and are some of the oldest in the brain. One of the most important is the thalamus, located in the heart of the cerebral hemispheres (thalamos is Greek for ‘inner chamber’). The thalamus is divided into two parts, one in each cerebral hemisphere. Each part looks rather like a football, with the long axis oriented from front to back. The thalamus performs two basic functions. The first, and most primitive, is similar to that of the cerebral cortex. Parts of the thalamus receive sensory information, other parts integrate the information, and still other parts assist in the control of movements through their influence on circuits of neurons in the brain stem. However, the second role of the thalamus, that of a relay station for the cortex, is even more important. As the cerebral hemispheres
evolved, the cerebral cortex grew in size and its significance for behavioural functions increased. The thalamus took on the function of receiving sensory information from the sensory organs, performing some simple analyses, and passing the results on to the primary sensory cortex. Thus, all sensory information (except for olfaction, which is the most primitive of all sensory systems) is sent to the thalamus before it reaches the cerebral cortex.
The hypothalamus Hypo- means ‘less than’ or ‘beneath’, and, as its name suggests, the hypothalamus is located below the thalamus, at the base of the brain. The hypothalamus is a small region, consisting of less than 1 cubic centimetre of tissue (smaller than a grape). Its relative importance far exceeds its relative size. The hypothalamus, like the brain stem, participates in homeostasis and species-typical behaviours. It receives sensory information, including information from receptors inside the organs of the body; thus, it is informed about changes in the organism’s physiological status. It also contains specialised sensors that monitor various characteristics of the blood that flows through the brain, such as temperature, nutrient content and amount of dissolved salts. In turn, the hypothalamus controls the pituitary gland, an endocrine gland attached by a stalk to the base of the hypothalamus. Hormones are chemicals produced by endocrine glands (from the Greek endo- ‘within’, and krinein ‘to secrete’). Endocrine glands secrete hormones into the blood supply, which carries them to all parts of the body. Hormones are similar to transmitter substances or neuromodulators, except that they act over much longer distances. Like transmitter substances and neuromodulators, they produce their effects by stimulating receptor molecules. These receptor molecules are located on (or in) particular cells. The presence of a hormone causes physiological reactions in these cells, which are known as target cells. Almost every cell of the body contains hormone receptors of one kind or other. This includes neurons; hormones that affect behaviour do so by altering the activity of particular groups of neurons in the brain. For example, the sex hormones have important effects on behaviour and are discussed in later chapters. The pituitary gland has been called the ‘master gland’ because the hormones it secretes act on target cells in other endocrine glands; thus, the pituitary gland controls the activity of other endocrine glands. By controlling the pituitary gland, the hypothalamus controls the entire endocrine system. Figure 4.34 shows some of the endocrine glands and the functions they regulate.
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Pituitary gland: control of kidneys, adrenal cortex, and ovaries or testes
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Thyroid gland: control of metabolism Parathyroid gland: control of mineral balance
Pancreas: control of carbohydrate metabolism Adrenal medulla (adrenalin and noradrenalin): breakdown of energy stores, increased blood pressure
Adrenal cortex (cortical steroid hormones): stress hormones
Testes (males): male development, control of production of sperms
Ovaries (females): Oestrogen – female development, control of menstrual cycles Progesterone – maintenance of pregnancy
Figure 4.34 The location and primary functions of the principal endocrine glands.
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The limbic system
yp The limbic system, a set of structures located sych in the cerebral hemispheres, plays an important role in learning and in the expression of emotion. Originally, this area was termed rhinenecephalon (or ‘smell brain’) because the areas within it were thought to be involved primarily in the sense of smell. The limbic system consists of several regions of the limbic cortex – the cerebral cortex located around the edge of the cerebral hemispheres where they join with the brain stem (limbus means ‘border’; hence the term ‘limbic system’). Besides the limbic cortex, the most important b
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temperature by causing sweating to occur, or it can raise it by causing shivering to occur. If these measures are inadequate, it can send messages to the cerebral cortex that will cause the person to engage in a learned behaviour, such as turning on an air conditioner or putting another log on the fire. Damage to the hypothalamus can cause impaired regulation of body temperature, changes in food intake, sterility and stunting of growth.
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The hypothalamus also controls much of the activity of the autonomic nervous system (ANS), which consists of nerves that control the functions of the glands activit ee and internal organs. The nerves of the autonomic nervous system control activities such as yp sych sweating, shedding tears, salivating, secreting digestive juices, changing the size of blood vessels (which alters blood pressure) and secreting some hormones. The autonomic nervous system has two branches. The sympathetic branch directs activities that involve the expenditure of energy. For example, activity of the sympathetic branch can increase the flow of blood to the muscles when we are about to fight someone or run away from a dangerous situation. The parasympathetic branch controls quiet activities, such as digestion of food. Activity of the parasympathetic branch stimulates the secretion of digestive enzymes and increases the flow of blood to the digestive system, as seen in Figure 4.35. The homeostatic functions of the hypothalamus can involve either internal physiological changes or behaviour. For example, the hypothalamus is involved in the control of body temperature. It can directly lower body h syc la
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Parasympathetic nervous system
Lachrymal glands: secretion of tears Pupil: dilation
Pupil: constriction
Sympathetic nervous system
Parasympathetic nervous system
Secretion of thick saliva
Secretion of thin saliva
Lachrymal gland
Salivary gland
Eye
Hair follicle
Blood vessels
Abdomen: constriction Muscles: dilation Skin: construction
Abdomen: constriction Muscles: constriction Skin: dilation
Sweating, piloerection (‘goose bumps’)
Sweat gland
Skin
Inhibition of contractions and secretion of stomach acid
Contractions, secretion of stomach acid
Faster rate of contraction
Slower rate of contraction
Stomach Heart Adrenal gland
Decreased activity
Increased activity
Secretion of adrenalin
Inhibition of contraction
Contraction
Ejaculation, orgasm
Intestines
Erection/vaginal lubrication
External genitalia
Bladder
Figure 4.35 The autonomic nervous system and the organs it controls.
components of the limbic system are the amygdala and the hippocampus. The amygdala and the hippocampus get their names from their shapes; amygdala means ‘almond’ and hippocampus means ‘sea horse’. Figure 4.36 shows a view of the limbic cortex, located on the inner surface of the cerebral hemisphere. The left hippocampus and amygdala, located in the middle of the temporal lobe, are shown projecting out into the place where the missing left hemisphere would be. You can also see the right hippocampus and amygdala, ‘ghosted in’.
The amygdala Damage to the amygdala, a cluster of neurons located deep in the temporal lobe, affects emotional behaviour, especially negative emotions such as those caused by painful, threatening or stressful events. Some patients are unable to recognise fear in a person’s voice or face (Adolphs et al., 1995, 1999; Morris et al., 1996). In a review of neuroimaging studies, however, Sergerie (2008) found that the amygdala responded to positive and nega-
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animal would be better off if it did not become ‘stressed out’ by unpleasant or threatening situations. However, research has shown that animals with damaged amygdalae cannot survive in the wild. The animals fail to compete successfully for food and other resources, and often act in ways that provoke attacks by other animals. The functions of amygdala are discussed further in Chapters 13 and 17.
Olfactory bulb
The hippocampus
Hypothalamus Amygdala Mammillary body
Hippocampus
Figure 4.36 Schematic drawing illustrating the structures of the limbic system. Source: From Pinel, J., Biopsychology, 3rd edn, © 1997. Published by Allyn and Bacon, Boston, MA. Copyright © by Pearson Education. By permission of the publisher.
tive emotional visual stimuli and responded more strongly to faces showing emotion than other emotional stimuli that were visual in nature. When the researchers looked at the data closely, they found that the effect sizes – the strength of the phenomenon under study – were larger for studies using positive than negative stimuli, a finding that is consistent with recent studies showing that although the neurons in the amygdala of monkeys respond to negative and positive stimuli, a greater number respond to positive than negative ones (Paton et al., 2006). While the review found no evidence of sex differences in this structure, another single study has found that, at rest, the right side of the amygdala showed greater connectivity with the rest of the brain in men; for women, the same pattern was found for the left side (Kilpatrick et al., 2006). Interestingly, the regions with which the right hemisphere showed connections were different from those with which the left hemisphere showed connections. Grezes et al. (2006) found that the amygdala (and a region called the human face area, described in Chapter 6) showed increased activity when people watched themselves being deceived. The authors attribute the increase to greater personal involvement by the participants when they make ‘emotional’ judgements that involve them – in this example, deceit is seen as a personal threat. The amygdala also controls physiological reactions that help provide energy for short-term activities such as fighting or fleeing (LeDoux, 1996). However, if these reactions are prolonged, they can lead to stress-related illnesses. If an animal’s amygdala is destroyed, the animal no longer reacts emotionally to events that normally produce stress and anxiety. We might think that an
The hippocampus (or hippocampal formation) is a collection of structures located just behind the amygdala, and plays an important role in memory. People with lesions of the hippocampus lose the ability to learn anything new (Milner et al., 1968; Keane et al., 1995). For them, ‘yesterday’ is always the time before their brain damage occurred; everything after that slips away, just as the memory of dreams often slips away from a person soon after awakening. The hippocampus and regions around it also seems to be responsible for navigating one’s way around certain types of route (Maguire et al., 1997, 1998). In healthy people whose brain activation is measured, this structure is selectively active when we have to find our way around a route, whether it is in our mind or in virtual space. The role of the hippocampus in memory is considered in more detail in Chapter 8.
The basal ganglia One final group of subcortical structures that is crucial to behaviour is the basal ganglia. The basal ganglia is the collective name for a group of nuclei, specifically, the globus pallidus, substantia nigra, striatum (made up of the caudate nucleus and putamen) and subthalamic nucleus (see Figure 4.37). Some of these receive inputs; some deliver output. The output nuclei, for example, send projections to the thalamus and two other subcortical regions (Utter et al., 2008) and these influence sensory and cognitive behaviour, the movement of the head and the eyes and some aspects of locomotion and posture. (And, as you’ve seen, deep brain stimulation in Parkinson’s disease targets these nuclei.) When the nuclei become dysfunctional, they can produce Parkinson’s (the dopamine neurons degenerate in the substantia nigra); the motor disorder, Huntington’s disease (remember this from the genetic counselling section from the last chapter) where the defective gene produces degeneration in neurotransmitter-specific neurons in the striatum; extreme of convoluted posture (dystonia); Tourette’s syndome (uncontrollable blinking and facial grimacing, plus
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Stimulating or inhibiting the release of transmitter substances
The basal ganglia
Some drugs stimulate certain terminal buttons to release their transmitter substance continuously, even when the axon is not firing. Other drugs prevent certain terminal buttons from releasing their transmitter substance when the axon fires. The effects of most of these drugs are more or less specific to one transmitter substance. Because different classes of neuron release different transmitter substances, these drugs affect only a selected set of neurons. An example of a stimulating drug is the venom of the black widow spider, which causes the release of a transmitter substance called acetylcholine, as illustrated by Figure 4.38. In contrast, botulinum toxin, a poison that is sometimes present in improperly canned food, prevents the release of acetylcholine. An adult will almost certainly survive the bite of a black widow spider; the symptoms are severe abdominal cramps. However, an extremely small amount of botulinum toxin – less than one-millionth of a gram – is fatal. The victim becomes paralysed and suffocates to death.
Stimulating or blocking postsynaptic receptor molecules
Figure 4.37 The location of the basal ganglia. Source: Science Photo Library Ltd.
Transmitter substances produce their effects by stimulating postsynaptic receptor molecules, which excite or inhibit postsynaptic neurons by opening ion channels and permitting ions to enter or leave the neurons. Some drugs duplicate the effects of particular transmitter substances by directly stimulating particular kinds of receptor mole-
coprolalia – vigorous, unpredictable and involuntary swearing); and obsessive-compulsive disorder (described in Chapter 18), possibly because of dysfunctional loops linking the striatum with the tip of the frontal lobe.
Drugs and behaviour activit
Terminal button
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Molecule of acetylcholine
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Communication between neurons involves the release of transmitter substances. Neurons yp release many different kinds of transmitter subh syc stance, and various drugs can affect the production or release of one or more of these chemicals. Drugs can also mimic the effects of transmitter substances on receptor molecules, block these effects, or interfere with the reuptake of a transmitter substance once it is released. Via these mechanisms, a drug can alter the perceptions, thoughts and behaviours controlled by particular transmitter substances. ee
Black widow spider venom causes acetylcholine to be released
Figure 4.38 Drugs that affect the release of a neurotransmitter, acetylcholine. Black widow spider venom causes acetylcholine to be released. Botulinum toxin prevents the release of acetylcholine from the terminal buttons.
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cules. If we use the lock-and-key analogy to describe the effects of a transmitter substance on a receptor molecule, then a drug that stimulates receptor molecules works like a master key, turning the receptor molecules on even when the transmitter substance is not present. For example, nicotine stimulates acetylcholine receptors located on neurons in certain regions of the brain (see Figure 4.39). In low doses, this stimulation has a pleasurable (and addictive) excitatory effect; in high doses, it can cause convulsions and death. Some drugs block receptor molecules, making them inaccessible to the transmitter substance and thus inhibiting synaptic transmission. A drug that blocks receptor molecules ‘plugs up’ the lock so that the key will no longer fit into it. A poison called curare, discovered by South American Indians, was used on the darts of their blowguns. This drug blocks the acetylcholine receptors that are located on muscle fibres. The curare prevents synaptic transmission in muscles. The paralysed victim is unable to breathe and consequently suffocates. Some medically useful chemicals work by blocking receptor molecules. For example, antipsychotic drugs alleviate the symptoms of schizophrenia, a serious mental disorder, by blocking receptor molecules in the brain that are normally stimulated by a transmitter substance called dopamine. This fact has led some investigators to suggest that the symptoms of schizophrenia may be caused by malfunctions of neurons that release dopamine. We dis-
Terminal button
cuss antipsychotic drugs later in this chapter and in Chapter 18 (Abnormal psychology).
Inhibiting reuptake The effects of most transmitter substances are kept brief by the process of reuptake. Molecules of the transmitter substance are released by a terminal button, they stimulate the receptor molecules in the postsynaptic membrane for a fraction of a second, and then they are pumped back into the terminal button. Some drugs inhibit the process of reuptake so that molecules of the transmitter substance continue to stimulate the postsynaptic receptor molecules for a long time. Therefore, inhibition of reuptake increases the effect of the transmitter substance. The excitatory effects of cocaine and amphetamine are produced by their ability to inhibit the reuptake of certain transmitter substances, including dopamine (see Figure 4.40).
Sedatives Some drugs depress behaviour, causing relaxation, sedation, or even loss of consciousness. These are called anti-anxiety or anxiolytic drugs. In most cases, the depression is caused by stimulation of a class of receptor molecules that is normally activated by neuromodulators produced by the brain. Barbiturates depress the brain’s activity by stimulating a particular category of neuromodulator receptors. In low doses, barbiturates have a calming effect. In progressively higher doses, they produce difficulty in walking and talking, unconsciousness, coma and death. Barbiturates are abused by people who want to achieve the relaxing, calming effect
Molecule of curare Molecule of nicotine
Molecule of acetylcholine
Terminal button
Transmitter substance is not taken back by the terminal button; therefore its effects on the receptor molecules are prolonged
Cocaine and amphetamine prevent reuptake Molecules of nicotine stimulation receptor molecules, duplicating the effects of acetylcholine
Molecules of curare block receptor molecules, preventing acetylcholine from stimulating them
Figure 4.39 Drugs that interact with receptor molecules in the postsynaptic membrane. Nicotine directly stimulates the receptor molecules. Curare blocks receptor molecules and thus prevents acetylcholine from activating them.
Figure 4.40 Drugs that block reuptake. Cocaine and amphetamine block the reuptake of certain transmitter substances, thus prolonging their effects on the receptor molecules in the postsynaptic membrane.
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of the drugs, especially to counteract the anxiety and irritability that can be produced by stimulants. They are occasionally prescribed as medication for sleep, but they are a poor choice for this purpose because they suppress dreaming and produce a particularly unrefreshing sleep. In addition, a dose of a barbiturate sufficient to induce sleep is not that much lower than a fatal dose. Ideally, the therapeutic dose of a drug is much lower than a fatal dose. Many anti-anxiety drugs are members of a family known as the benzodiazepines, which include the wellknown tranquilliser Valium (diazepam). These drugs, too, stimulate some sort of neuromodulator receptors located on neurons in various parts of the brain, including the amygdala. The benzodiazepines are effective in reducing anxiety and are sometimes used to treat people who are afflicted by periodic attacks of severe anxiety. In addition, some benzodiazepines serve as sleep medications. These behavioural effects suggest that they mimic the effects of neuromodulators involved in the regulation of mood and the control of sleep.
By far the most commonly used depressant drug is ethyl alcohol, the active ingredient in alcoholic beverages. This drug has effects similar to those of the barbiturates: larger and larger doses of alcohol reduce anxiety, disrupt motor coordination and then cause unconsciousness, coma and finally death. The effects of alcohol and barbiturates are additive: a moderate dose of alcohol plus a moderate dose of barbiturates can be fatal. The primary effect of alcohol appears to be similar to that of the benzodiazepines: it stimulates some type of neuromodulator receptor. Suzdak et al. (1986) discovered a drug that reverses alcohol intoxication, presumably by blocking some type of neuromodulator receptor. Although the behavioural effects of alcohol may be mediated by neuromodulator receptors, alcohol has other, potentially fatal effects on all cells of the body. Alcohol destabilises the membrane of cells, interfering with their functions. Thus, a person who takes some of the anti-alcohol drug could go on to drink themselves to death without becoming drunk in the process.
Controversies in Psychological Science – What is drug addiction? The issue Some drugs have very potent reinforcing effects, which lead some people to abuse them or even to become addicted to them. Robbins and Everitt (1999) report that the annual costs of drug addiction in the USA alone stand at around $80 billion. Many people – psychologists, health professionals and lay people – believe that ‘true’ addiction is caused by the unpleasant physiological effects that occur when an addict tries to stop taking the drug. For example, Eddy et al. (1965) defined physical dependence as ‘an adaptive state that manifests itself by intense physical disturbances when the administration of a drug is suspended’ (p. 723). In contrast, they defined psychic dependence as a condition in which a drug produces ‘a feeling of satisfaction and a psychic drive that requires periodic or continuous administration of the drug to produce pleasure or to avoid discomfort’ (p. 723). Most people regard the latter as less important than the former. But, as we shall see, the reverse is true.
The evidence Robbins and Everitt suggest that ‘drug dependence and addiction can be partly understood as gradual adaptations of the brain to chronic drug exposure’. But other psychological factors also influence drug-taking, from finding the drugs, to the motivation for using them, to being able to live without them.
For many years, heroin addiction has been considered as the prototype for all drug addictions. People who habitually take heroin (or other opiates) become physically dependent on the drug, that is, they show tolerance and withdrawal symptoms. Tolerance is the decreased sensitivity to a drug that comes from its continued use; the drug user must take larger and larger amounts of the drug in order for it to be effective. Once a person has taken an opiate regularly enough to develop tolerance, that person will suffer withdrawal symptoms if they stop taking the drug. Withdrawal symptoms are primarily the opposite of the effects of the drug itself. For example, heroin produces euphoria; withdrawal from it produces dysphoria – a feeling of anxious misery (euphoria and dysphoria mean ‘easy to bear’ and ‘hard to bear’, respectively). According to Freud, this was ‘agony beyond human power to bear’. Heroin produces constipation; withdrawal from it produces nausea, cramping and diarrhoea. Heroin produces relaxation; withdrawal from it produces agitation. Most investigators believe that the withdrawal symptoms are produced by the body’s attempt to compensate for the unusual condition of heroin intoxication. That is, most systems of the body, including those controlled by the brain, are regulated so that they stay at an optimal value. When a drug artificially changes these systems for a prolonged time, home-
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Controversies in Psychological Science – Continued ous drug, not in the same league as heroin. Obviously, they were wrong; cocaine is even more addictive than heroin. As a matter of fact, laboratory animals who can press a lever and give themselves injections of cocaine are more likely to die than are those who can give themselves injections of heroin. Secondly, some drugs produce physical dependence (tolerance and withdrawal symptoms) but are not abused (Jaffe, 1985). The reason why they are not abused is that they do not have reinforcing effects on behaviour – they are just not any fun to take. People take drugs because they enjoy them. And the more they like them, the more excessive their drug-taking (Ahmed, 2005). Studies in rodents suggest that the greater the access to cocaine, the greater the rat’s drug-seeking behaviour (Vanderschuren and Everitt, 2004). A three month exposure to a drug led to rats being unable not to seek drugs, even when they were punished for doing so (DerocheGamonet et al., 2004). Rats exposed to heroin daily had lower and more stable levels of drug intake than those who were exposed to it for 24 hours (Kenny et al., 2006). As the drugtaking increases, the excitability of the reward systems, reflected in brain activation and neurotransmitter release, decreases. Therefore, more of the drug is needed to resume this level of excitability (Kenny, 2007). Similarly, neuroimaging data from adults has shown that activation in the insula, prefrontal cortex and anterior cingulate cortex is associated with urges to take a drug, whether cigarettes, heroin, alcohol or cocaine (Naqvi and Bechara, 2008). Ultimately drugs ‘work’ by stimulating the release of dopamine from the brain stem tegmental area (Naqvi and Bechara, 2008). A study by Kirby et al. (1999) tested a specific model of substance abuse which suggests that the value of a reward is affected by the length of time between the promise of that reward and actually obtaining it. For example, if a reward was promised a long time in the future, then its present value would be small. If a competing reward was made available sooner, this would be chosen over the other. This is called delay-discounting. This is relevant to drug use because the delay-discounting model of impulsive behaviour would suggest that impulsive individuals would choose a smaller, immediate reward rather than wait for a larger reward promised after a longer delay. Kirby et al. put this hypothesis to the test in an experiment in which 56 heroin addicts and 60 drug-free controls had to make a choice between either receiving an $11–80 reward available immediately, or receiving a larger reward ($25–85) after a delay from one week to six months. There was a one in
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ostatic mechanisms begin to produce the opposite reaction, which partially compensates for the disturbance from the optimal value. These compensatory mechanisms account for the fact that more and more heroin must be taken in order to achieve the effects that were produced when the person first started taking the drug. They also account for the symptoms of withdrawal: when the person stops taking the drug, the compensatory mechanisms make themselves felt, unopposed by the action of the drug. Heroin addiction has provided such a striking example of drug dependence that some authorities have concluded that ‘real’ addiction does not occur unless a drug causes tolerance and withdrawal. Withdrawal symptoms make it difficult for a person to stop taking heroin – they help keep the person hooked. But withdrawal symptoms do not explain why a person becomes a heroin addict in the first place; that fact is explained by the drug’s reinforcing effect. Certainly, people do not start taking heroin so that they will become physically dependent on it and feel miserable when they go without it. Instead, they begin taking it because it makes them feel good. Even though the withdrawal effects of heroin make it difficult to stop taking the drug, these effects alone are not sufficient to keep most people hooked (Baker et al., 2006). In fact, when the cost of the habit gets too high, some addicts who stop taking heroin experience ‘cold turkey’. Doing so is not as painful as most people believe; withdrawal symptoms have been described as similar to a bad case of influenza – unpleasant, but survivable. Mood declines – people feel unstable, stressed, anxious and depressed (Baker et al., 2006). After a week or two, when their nervous systems adapt to the absence of the drug, these addicts recommence their habit, which now costs less to sustain. However, addicts do cite a fear of withdrawal symptoms as being one reason why they are motivated to continue taking drugs (the effects of withdrawal from a drug like ethanol, for example, include tremors and convulsions). The strength of withdrawal is not related to the strength of relapse. The reason why people take – and continue to take – drugs such as heroin is that the drugs give them a pleasurable ‘rush’; in other words, the drugs have a reinforcing effect on their behaviour. There are two other lines of evidence that contradict the assertion that drug addiction is caused by physical dependence. First, some potent drugs, including cocaine, do not produce physical dependence. That is, people who take the drug do not show tolerance; and if they stop, they do not show any withdrawal symptoms. As a result, experts believed for many years that cocaine was a relatively innocu-
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Controversies in Psychological Science – Continued six chance of winning the reward in each trial. The researchers found that heroin addicts were twice as likely as controls to discount delayed rewards in favour of immediate ones. They suggest that these findings are important for treatment interventions that focus on the consequences of drug abuse (such as going to jail, losing a family, failing to get a job, developing HIV) because such consequences may not be particularly salient to the addict. Programmes which provide rewards after short periods of abstinence, Kirby et al. argue, should be more effective in preventing drug use because the reward would be immediate and not delayed.
Stimulants Several categories of drugs stimulate the central nervous system and thus activate behaviour. Because of the effects some of these drugs have on the neural circuits involved in reinforcement (reward), they tend to be abused. Two popular stimulant drugs, amphetamine and cocaine, have almost identical effects: they inhibit the reuptake of dopamine and thus strengthen the effectiveness of synapses that use this transmitter substance. As you will see in Chapter 13, reinforcing stimuli – such as food for a hungry animal, water for a thirsty one, or sexual contact for a sexually aroused one – exert their behavioural effects largely by increasing the activity of a circuit of dopamine-secreting neurons. Thus, amphetamine and cocaine mimic the effects of reinforcing stimuli. Free-base cocaine (crack) is particularly addictive. The drug has an immediate effect on the reuptake of dopamine and produces such a profound feeling of euphoria and pleasure that the person wants to repeat the experience again and again. Cocaine and amphetamine, if taken in large enough doses for a few days, can produce the symptoms of paranoid schizophrenia – a serious mental disorder described in Chapter 18. Heavy users of these drugs suffer from hallucinations and their thoughts become confused and difficult to control. They may come to believe that they are being attacked or plotted against. In fact, an experienced clinician cannot distinguish the drug-induced symptoms from those that occur in people who really have the psychosis. This fact has suggested to some investigators that schizophrenia may be caused by overactivity of dopaminesecreting synapses. Opiate drugs have both excitatory and inhibitory effects on behaviour. All of these effects occur because
Conclusion The most important lesson we can learn from the misguided distinction between ‘physiological’ and ‘psychological’ addiction is that we should never underestimate the importance of psychological factors. Given that behaviour is controlled by circuits of neurons in the brain, even psychological factors involve physiological mechanisms. People often pay more attention to physiological symptoms than psychological ones – they consider them more real. But behavioural research indicates that an exclusive preoccupation with physiology can hinder our understanding of the causes of addiction.
these drugs mimic the effects of the body’s own opioid neuromodulators: they stimulate opioid receptors located on neurons in various parts of the brain. The inhibitory effects include analgesia (reduced sensitivity to pain), hypothermia (lowering of body temperature) and sedation. The pain reduction is accomplished by neurons in the midbrain, the hypothermia by neurons in the hypothalamus and the sedation by neurons in the medulla. A fatal overdose of an opiate kills its victim by inhibiting the activity of circuits of neurons in the medulla that control breathing, heart rate and blood pressure. But it is the excitatory effects of opiates that induce people to abuse them. Some opioid receptors are located on dopaminesecreting neurons involved in reinforcement (reward). When a person takes an opiate such as heroin, the activity of these neurons produces feelings of euphoria and pleasure, similar to those produced by cocaine or amphetamine. These excitatory effects, and not the inhibitory ones, are responsible for addiction.
Drugs and altered states of consciousness Throughout history, people have enjoyed changing their consciousness now and then by taking drugs, fasting, meditating or chanting. Even children enjoy spinning around and making themselves dizzy – presumably for the same reasons. Chemicals found in several different plants produce profound changes in consciousness. Behaviourally, these changes are difficult to specify. Large doses of drugs such as marijuana or LSD tend to sedate laboratory animals, but the animals give no sign of having their consciousness altered. Only humans can describe the consciousness-altering effects of the drugs. In Doors of
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Perception, Aldous Huxley described the intense vision he experienced on looking at a bowl of flowers. The experience was induced by a synthetic form of the drug mescaline (derived from cactus peyote), which has been used by shamans for centuries as religious communion.
[Plato] could never, poor fellow, have seen a bunch of flowers shining with their own inner light and all but quivering under the pressure of the significance with which they were charged; could never have perceived that what rose and iris and carnation so intensely signified was nothing more, and nothing less, than what they were – a transience that was yet eternal life, a perpetual perishing that was at the same time pure Being, a bundle of minute, unique particulars in which, by some unspeakable and yet self-evident paradox, was to be seen the divine source of all existence. I continued to look at the flowers, and in their living light I seemed to detect the qualitative equivalent of breathing – but of a breathing without returns to a starting point, with no recurrent ebbs but only a repeated flow from beauty to heightened beauty, from deeper to ever deeper meaning.
when we are asleep, in a particular stage called REM sleep (because of the rapid eye movements that occur then). During the rest of the day, circuits of serotoninsecreting neurons inhibit the mechanisms responsible for dreaming, thus preventing them from becoming active. Drugs such as LSD, psilocybin and dimethyltryptamine (DMT) suppress the activity of serotonin-secreting neurons, permitting dream mechanisms to become active. As a result, hallucinations occur. These hallucinations are often interesting and even awe-inspiring, but sometimes produce intense fear and anxiety. Not all hallucinogenic drugs interfere with serotoninsecreting synapses. Cocaine and amphetamine, which affect dopamine-secreting synapses, also produce hallucinations. However, the hallucinations produced by cocaine and amphetamine take some time to develop, and they are primarily auditory. LSD-induced hallucinations take place immediately and are primarily visual, as dreams are. The two types of hallucination undoubtedly occur for different reasons.
Source: Aldous Huxley (1954), The Doors of Perception.
More famously, Samuel Taylor Coleridge wrote Kubla Khan after a drug-taking session:
In the Summer of the year 1797, the Author. . . had retired to a lonely farmhouse between Porlock and Linton, on the Exmoor confines of Somerset and Devonshire. In consequence of a slight indisposition, an anodyne had been prescribed, from the effects of which he fell asleep in his chair at the moment he was reading. The Author continued for about three hours in a profound sleep, at least of the external senses, during which time he has the most vivid confidence, that he could not have composed less than from two hundred to three hundred lines. . . on awaking he appeared to himself to have a distinct recollection of the whole, and . . . instantly and eagerly wrote down the lines that are here preserved. Source: Samuel Taylor Coleridge, prefatory note to Kubla Khan (1797).
Drugs can affect consciousness in several different ways. We have the clearest understanding of one category of drugs: those that affect synapses that use a transmitter substance called serotonin. Serotonin plays an important role in the control of dreaming. Normally, we dream only
Aldous Huxley. Source: Hulton Archive/Getty Images.
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Tetrahydrocannabinol (THC), the active ingredient in marijuana, exerts its behavioural effects by stimulating THC receptors, specific neuromodulator receptors present in particular regions of the brain. THC produces analgesia and sedation, stimulates appetite, reduces nausea caused by drugs used to treat cancer, relieves asthma attacks, decreases pressure within the eyes in patients with glaucoma, and reduces the symptoms of certain motor disorders. On the other hand, THC interferes with concentration and memory, alters visual and auditory perception, and distorts perceptions of the passage of time (Howlett, 1990).
Drug classification
On the advice of the novelist Aldous Huxley, Timothy Leary, then a clinical psychologist at Harvard, took his first acid trip and reported its effect. He took lysergic acid (LSD), a powerful psychotropic drug derived from a fungus (ergot) and synthesised in the laboratory in 1930. Source: Ben Martin/Time Life Pictures/Getty Images.
In the UK, controlled susbstances (drugs) are classified as either A, B or C. Class A drugs are those most likely to cause harm and include LSD, heroin and cocaine. Class B drugs are considered to be not as harmful and include amphetamines, Ritalin and cannabis. In the US, cannabis is deemed a Schedule 1 substance – it has the potential to be ‘abused’ and has no medical use. Class C drugs include ketamine, painkillers and various other drugs that require a prescription. Cannabis or marijuana is one of the most commonly used, if not the most commonly used prohibited drug in existence. According to one recent UK survey, marijuana was the most commonly experienced drug (87 per cent), followed by cocaine at 35 per cent (Observer Drugs, 2008). The 2006 National Survey on Drug Use and Health in the US estimated that 98 million Americans over 12 years of age had tried it at least once (the figure represents 40 per cent of the population). Between 71 and 77 per cent of US prisoners claimed to have used the drug at some point (Bureau of Justice Statistics, 2006). As the International Perspective below shows, it is also commonly used by 18–25-year-olds.
The psychology of cannabis use – An international perspective Cannabis is a drug derived from the plant genus Cannabis and comprises around 400 compounds. The most potent of these is tetrahydrocannabinol (THC), one of the 60 cannabinoids the plant contains, and a typical joint will contain between 150 and 300 mg of THC. Surveys of UK universities show that around 50–60 per cent of respondents report having used cannabis (Ashton, 2001). A study of 1,261 Australian adolescents aged between 13 and 17 years found that a quarter of the sample reported having used cannabis and this use increased with age (Rey et al., 2002). A glance at Figure 4.41 shows that people who are heavy users of cannabis also
report higher levels of depression than do light users (Rey et al., 2002). While cannabis has been used recreationally for centuries to elevate mood, recent controversy has surrounded the use of cannabis to alleviate pain. One reason why the drug may be inappropriate is that it may have psychological consequences that could be either harmful or dangerous. About 50 per cent of THC in a joint of cannabis is inhaled through smoke (the amount is less when taken orally). Because THC has a half-life of seven days, it can remain vital for up to 30 days which means that traces of cannabis can be detected in the body up to a month after inhalation/ingestion.
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The psychology of cannabis use – Continued 60
Ever used cannabis (%)
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Figure 4.41 The relationship between cannabis use and depression scores in over 4,000 Australian adolescents. Source: Rey, J.M., Sawyer, M.G., Raphael, B., Patton, G.C. and Lynskey, M., Mental health of teenagers who use cannabis. British Journal of Psychiatry, 2002, 150, 216–21, reprinted by permission of the Royal College of Psychiatrists.
The behavioural effects of cannabis are varied. It can stimulate appetite, reduce anxiety and create psychedelic experiences. Doses of THC as low as 2.5 g in herbal cigarettes can produce a feeling of intoxication and a reduction in anxiety (Ashton, 2001). It can also produce panic attacks and paranoia. Its effects on psychomotor performance are similar to those of alcohol: behaviour becomes uncoordinated and reaction time slows. In many European countries, the second most common substance found in the bodies of drivers involved in fatal accidents or in drivers who drive poorly is cannabis. The majority of those who use cannabis show no evidence of excessive or illegal alcohol consumption. Similar performance decrements are seen in pilots (even pilots who are regular cannabis users) 24 hours after cannabis intake. The association between cannabis use and the development of psychotic disorders, such as schizophrenia, is a controversial one. Many studies have reported that psychotic symptoms can occur but that these are short-lived; few studies have followed up such patients, however, to examine the long-term consequences of cannabis use. A study of 535 Danish patients who had been treated for cannabis-induced psychotic symptoms (Arendt et al., 2005) found that 44 per cent of cases showed schizophrenia-type symptoms. Some 77
per cent of the sample reported new psychotic symptoms. Approximately 47 per cent of the sample received a diagnosis of cannabis-induced schizophrenia a year after seeking treatment for cannabis-related psychosis. The authors caution, however, that there was a significant delay in the majority of patients in the development of schizophrenia-type symptoms. They also note that they were unable to control for any other type of substance use during the follow-up period. Between 40–51 per cent of patients with schizophrenia have used cannabis (Borsani et al., 2002; Barnett et al., 2007) and there appears to be an association between decreased grey matter and cannabis use in schizophrenia patients who are cannabis users and have had their first episode (Bangalore et al., 2008). (In psychiatry, an episode is one serious experience or appearance of a disorder.) Recent debate in some European countries has centred on the therapeutic effects of cannabis. Cannabis was a drug recommended for various ills as long as 5,000 years ago in China. A review by Robson (2001) describes how, historically, cannabis mixed with wine was recommended as a surgical analgesic. In nineteenth-century Britain, the use of cannabis for the alleviation of illness was common. Even Queen Victoria’s physician lauded cannabis’s ability to relieve physical ailments. There is some evidence for cannabis’s therapeutic effects. Patients with cancer frequently report a reduction in the feeling of nausea that is induced by chemotherapy (Robson, 2001). Questionnaire studies of British and American multiple sclerosis sufferers show that cannabis smokers report reduced muscle spasm, increased pain relief, improvement in balance and an improvement in memory. Since 2001, however, the US Congress has ruled that the drug has no medical value. Cannabis use is legal in some European countries but in restricted contexts. Danish law states that cannabis is illegal but has a provision that condones possession or sale of up to 30 g of cannabis (MacCoun and Reuter, 2001). This level, set in 1976, was reduced to 5 g in 1985. Around 1,200 coffee shops sell cannabis in the Netherlands and operate according to strict guidelines (such as no advertising, no public disturbances, no sales to minors, and so on). Because of cannabis’s status as an illegal drug in some European countries, especially the United Kingdom, much debate has surrounded the legitimacy of this position, with a number of doctors and patients questioning the decision to restrict or prohibit its use.
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Chapter review The brain and its components
• Neuropsychologists study the effects of brain damage on
• The brain has two major functions: to control behaviour and to regulate the body’s physiological processes.
• The central nervous system (CNS) consists of the spinal cord
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and the three major divisions of the brain: the brain stem, the cerebellum and the cerebral hemispheres. The cerebral cortex, which covers the cerebral hemispheres, is wrinkled by fissures and gyri. The brain communicates with the rest of the body through the peripheral nervous system, which includes the spinal nerves and cranial nerves. The basic element of the nervous system is the neuron. Neurons are assisted in their tasks by glia, which provide physical support, aid in the development of the nervous system, provide neurons with chemicals they need, remove unwanted chemicals, provide myelin sheaths for axons and protect neurons from infection. One neuron communicates with another (or with muscle or gland cells) by means of synapses. A synapse is the junction of the terminal button of the presynaptic neuron with the membrane of the postsynaptic neuron. Synaptic communication is chemical; when an action potential travels down an axon, it causes a transmitter substance to be released by the terminal buttons. An action potential consists of a brief change in the electrical charge of the axon, produced by a brief entry of positively charged sodium ions into the axon followed by a brief exit of positively charged potassium ions. Ions enter the axon through ion channels, and ion transporters eventually restore the proper concentrations of ions inside and outside the cell. Molecules of the transmitter substance released by terminal buttons either excite or inhibit the firing of the postsynaptic neuron. The combined effects of excitatory and inhibitory synapses on a particular neuron determine the rate of firing of that neuron. Neuromodulators resemble transmitter substances but travel further and are dispersed more widely. They are released by terminal buttons and modulate the activity of many neurons. The best-known neuromodulators are the opioids, which are released when an animal is engaged in essential, meaningful behaviour. The opiates, extracted from the sap of the opium poppy or produced in a laboratory, stimulate the brain’s opioid receptors.
Techniques for studying the brain • Various techniques are available for neuroscientists to investigate brain function. These include experimental lesion, observing the effects of natural or accidental brain damage, recording the electrical activity of the brain or observing its structure or metabolic activity.
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people’s behaviour, correlating their behavioural deficits with the location of their lesions. The assessment of cognitive impairment after brain injury is called neuropsychological assessment. Neuropsychological rehabilitation refers to a programme of remediation that helps the patient regain some of the function lost through brain injury. Techniques used to measure activity of the peripheral nervous system or autonomic nervous system included galvanic skin response (GSR), electrocardiography (ECG) and electromyography (EMG). GSR is a measure of arousal indexed by electrodermal response; ECG is a measure of heart rate; EMG is a measure of muscle activity. Sophisticated methods of observing brain structure and activity in healthy individuals include computerised tomography (CT), positron emission tomography (PET), magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI). CT allows us to view the brain’s structure; PET permits researchers to study the neural activity of specific regions of the living human brain. MRI is a measure of brain structure and provides clearer images of the brain’s structure than does CT; fMRI is a measure of brain activity. Psychophysiologists measure the brain’s electrical activity using electroencephalography (EEG) and event-related potentials (ERP). Magnetoencephalography (MEG) records changes in magnetic fields generated by neurons. Repetitive transcranial magnetic stimulation (rTMS) involves passing a magnetic current over the head and exciting the cortex; this often results in temporary impairment of cognitive function or an alleviation of depressive symptoms.
Control of behaviour • Anatomically, the cerebral cortex is divided into four lobes: frontal, parietal, occipital and temporal.
• Functionally, the cerebral cortex is organised into five major regions: the three regions of the primary sensory cortex (visual, auditory and somatosensory), the primary motor cortex and the association cortex. • The association cortex consists of sensory regions that are responsible for perceiving and learning and motor regions that are responsible for planning and acting. • Visual stimulation is transmitted from the eyes to the brain through the optic nerves, one of the pairs of cranial nerves. The information is sent to the primary visual cortex in the occipital lobe. • The motor association cortex in the frontal lobe is responsible for planning activity; the primary motor cortex is responsible for initiating movement.
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• Somatosensory information is transmitted from the skin to the
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spinal cord by means of a spinal nerve. It is then sent up through the spinal cord and is relayed to the primary somatosensory cortex. Lateralisation refers to whether a function is localised in the left or right hemisphere. The right and left hemispheres are involved with somewhat different functions: the left is superior at reading, speech production and speech comprehension; the right hemisphere is superior for visuospatial ability and recognition of emotion. The two cerebral hemispheres are connected by a large bundle of axons called the corpus callosum which allows the hemispheres to transfer information to one another. The frontal lobe is concerned with motor functions, planning strategies for action, working memory, emotion and problemsolving. A region of the left frontal cortex (Broca’s area) is specialised for the control of speech. Somatosensory information is processed by the parietal lobe, visual information by the occipital and lower temporal lobes, and auditory information by the upper temporal lobe. Other functions of these lobes are related to these perceptual processes; for example, the parietal lobes are concerned with perception of space and knowledge about the body as well as mental arithmetic.
Control of internal functions and automatic behaviour
nervous system, or it can cause neural circuits in the cerebral cortex to execute more complex, learned behaviour. • The amygdala and the hippocampus are both located within the temporal lobe, specifically within the limbic system. The amygdala is involved in various emotional processes including fear conditioning. • The hippocampus is involved in learning and memory; people with damage to this structure can recall old memories but are unable to learn anything new.
Drugs and behaviour • Many chemicals found in nature have behavioural effects, and many more have been synthesised in the laboratory.
• Drugs can facilitate or interfere with synaptic activity. Facilitators
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species-typical behaviours. The brain stem, which consists of the medulla, the pons and the midbrain, contains neural circuits that control vital physiological functions and produce automatic movements such as those used in locomotion, fighting and sexual behaviour. The cerebellum assists the cerebral cortex in carrying out movements; it coordinates the control of muscles, resulting in smooth movements. It also regulates postural adjustments and appears to play some role in cognition and reading impairment. The thalamus participates in the control of movement and relays sensory information to the cerebral cortex. The hypothalamus receives sensory information from sense receptors elsewhere in the body and also contains its own specialised receptors, such as those used to monitor body temperature. It controls the pituitary gland, which, in turn, controls most of the endocrine glands of the body, and it also controls the internal organs through the autonomic nervous system. Hormones, secreted by endocrine glands, are chemicals that act on hormone receptors in target cells and produce physiological reactions in these cells. The hypothalamus can control homeostatic processes directly and automatically through its control of the pituitary gland and the autonomic
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include drugs that cause the release of a transmitter substance (such as the venom of the black widow spider); drugs that directly stimulate postsynaptic receptor molecules, thus duplicating the effects of the transmitter substance itself (such as nicotine); and drugs that inhibit the reuptake of a transmitter substance (such as amphetamine and cocaine). Drugs that interfere with synaptic activity include those that inhibit the release of a transmitter substance (such as botulinum toxin) and those that block receptor molecules (such as curare). There are several major categories of drugs that affect behaviour. Alcohol, barbiturates and tranquillisers depress the activity of the brain by stimulating various types of receptor molecule. Amphetamine and cocaine stimulate the brain primarily by retarding the reuptake of dopamine. The opiates duplicate the effects of the brain’s opioids, decreasing sensitivity to pain and producing intensely enjoyable feelings of euphoria and pleasure. LSD, psilocybin and related drugs inhibit the activity of synapses that use serotonin. The hallucinogenic effects of these drugs may be related to dreaming, which is controlled by circuits of serotonin-secreting neurons. The physiological effects of marijuana are produced by a compound called THC which stimulates receptors that are normally activated by a natural neuromodulator called anandamide. Psychotherapeutic drugs include those that reduce the symptoms of schizophrenia and those that relieve depression. Anti-schizophrenic drugs block dopamine receptors, and antidepressant drugs generally facilitate the action of serotonin. Opiates produce tolerance and withdrawal symptoms, which make their habitual use increasingly expensive and make quitting more difficult. The primary reason for addiction is the reinforcing effect, not the unpleasant symptoms produced when an addict tries to quit. Tolerance appears to be produced by homeostatic mechanisms that counteract the effects of the drug.
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Suggestions for further reading Psychobiology and neuroscience – general reading
Methods
Carlson, N.R. (2010) Physiology of Behaviour (10th edn). Boston: Allyn & Bacon. DeVries, A.C. and Nelson, R.J. (2009) Current Directions in Biological Psychology. Boston: Allyn & Bacon. Martin, G.N. (2003) Essential Biological Psychology. London: Arnold. Martin, G.N. (2006) Human Neuropsychology (2nd edn). Harlow: Pearson Education. Toates, F. (2006) Biological Psychology (2nd edn). Harlow: Pearson Education. Wickens, A. (2009) Introduction to Biopsychology (3rd edn). Harlow: Pearson Education. These are good, comprehensive introductions to the physiology of behaviour, the relationship between human brain activity, structure and function, and general psychobiology.
Andreassi, J.L. (2001) Psychophysiology (4th edn). Hillsdale, NJ: Lawrence Erlbaum Associates. Beaulieu, A. (2002) A space for measuring mind and brain: Interdisciplinarity and digital tools in the development of brain mapping and functional imaging, 1980–1990. Brain and Cognition, 49, 13–33. Cabeza, R. and Nyberg, L. (1997) Imaging cognition: An empirical review of PET studies with normal subjects. Journal of Cognitive Neuroscience, 9, 1, 1–26. Cabeza, R. and Nyberg, L. (2000) Imaging cognition II: An empirical review of 275 PET and fMRI studies. Journal of Cognitive Neuroscience, 12, 1, 1–47. Grafton, S.T., Sinnott-Armstrong, W.P., Gazzaniga, S.I. and Gazzaniga, M.S. (2007) Brain scans go legal. Scientific American Mind, 17, 6, 30–37. Raichle, M.E. (2008) A brief history of human brain mapping. Trends in Neurosciences, 32, 2, 118–26. Andreassi’s book is the most well-known general introduction to psychophysiology. Raichle and Beaulieu’s articles review the development of the techniques. The Cabeza and Nyberg articles review, and give a more critical account of, the contribution of PET and fMRI studies to neuropsychology.
The development of neuroscience Finger, S. (2000) Minds behind the brain. Oxford: Oxford University Press. Kandel, E.R. and Squire, L.R. (2000) Neuroscience: Breaking down scientific barriers to the study of brain and mind. Science, 290, 1113–20. Two very good items on the history of neuroscience.
Localisation and lateralisation of function Cowey, A. (2001) Functional lateralization of the brain. The Psychologist, 14, 5, 250–54. Springer, S.P. and Deutsch, G. (2001) Left Brain, Right Brain (5th edn). New York: W.H. Freeman. Excellent accounts of lateralisation of function. Springer and Deutsch’s book is probably the best book reviewing functional lateralisation.
Basic neuroanatomy and neurophysiology England, M.A. and Wakeley, J. (1991) A Colour Atlas of the Brain and Spinal Cord. Aylesbury: Wolfe. Kosslyn, S.M., Cacioppo, J.T., Davidson, R.J., Hugdahl, K., Lovallo, W.R., Spiegel, D. and Rose, R. (2002) Bridging psychology and biology. American Psychologist, 57, 5, 341–51. Swanson, L.W. (2002) Brain Architecture: Understanding the basic plan. Oxford: Oxford University Press. A number of books cover the neuroanatomy and neurophysiology of the brain and the items listed here cover most of these two topics and do it well.
Drugs and behaviour Baker, T.B., Japuntich, S.J., Hogle, J.M., McCarthy, D.E. and Curtin, J.J. (2006) Pharmacologic and behavioural withdrawal from addictive drugs. Current Directions in Psychological Science, 15, 5, 232–36. Crombag, H.S. and Robinson, T.E. (2004) Drugs, environment, brain and behavior. Current Directions in Psychological Science, 13, 3, 107–11. Grilly, D.M. (2006) Drugs and Human Behaviour (5th edn). Boston: Allyn & Bacon. Hobson, J.A. (2005) The Dream Drugstore: Chemically altered states of consciousness. Cambridge, MA: MIT Press. Julien, R.M.A. (2007) A Primer of Drug Action (11th edn). San Francisco: W.H. Freeman. Naqvi, N.H. and Bechara, A. (2008) The hidden island of addiction: the insula. Trends in Neurosciences, 32, 1, 56–67. Parrott, A., Morinian, A., Moss, M. and Scholey, A. (2003) Understanding Drugs and Behaviour. Chichester: Wiley. Robinson, T.E. and Berridge, K.C. (2003) Addiction. Annual Review of Psychology, 54, 25–54. Julien’s book is probably the best introductory book on drugs and the biochemistry of drug use available. Parrott et al.’s book focuses not only on the psychopharmacology of drug use – from tobacco to ecstasy – but on the health and social consequences of drug use. The other items give very good overviews of drugs and addiction.
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WEBSITE ADDRESSES
Journals to consult Addiction
Journal of Cognitive Neuroscience
Biological Psychology
Journal of Psychopharmacology
Brain
Nature Neuroscience
Brain and Cognition
Neuroimage
Brain and Language
Neuropsychologia
British Journal of Neuropsychology
Neuropsychology
British Medical Journal
Psychobiology
Cerebral Cortex
Psychoneuroendocrinology
Cognitive Neuropsychology
Psychophysiology
Cortex
Science
Current Opinion in Neurobiology
Trends in Neuroscience
International Journal of Neuroscience
Trends in Pharmacological Sciences
International Journal of Psychophysiology
Website addresses http://www.psychology.org/links/Paradigms_and_Theories/ Neuroscience/ An excellent collection of links to neuroscience sites. http:://www.functionalmri.org/ A collection of links to fMRI sites and other neuroscience-related topics. http://pegasus.cc.ucf.edu/~Brainmd1/brain.html An internet tutorial on parts of the brain and what they do. http://www.med.harvard.edu/AANLIB/home.html An excellent brain atlas site from the University of Harvard Medical School.
http://www.psychologie.uni-bonn.de/online-documents/lit_pp.htm Allows you access to full-text versions of articles on psychophysiology. http://www.neuropsychologycentral.com A link to an excellent collection of neuroscience links. http://www.bigbluedesign.com/quest/addgene.html A site which considers evidence for an ‘alcoholic’ gene. http://www.rci.rutgers.edu/~lwh/drugs/ A link to an online book, Drugs, Brains and Behaviour, by Robin Timmons and Leonard Hamilton.
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You really can smell fear, say scientists James Randerson, Science correspondent
The smell of fear, one of the most terrible clichés of pulp fiction, is actually founded in fact, scientists claim today. People can unconsciously detect whether someone is stressed or scared by smelling a chemical pheromone released into their sweat, according to researchers who have investigated the underarm secretions of petrified skydivers. The team found that the smell of fear triggered a heightened response in brain regions associated with fear when inhaled by volunteers in a brain scanner. The research suggests that, like many animal species, humans can detect and subconsciously respond to pheromones released by other people.
CHAPTER 5
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Source: from ‘You really can smell fear, say scientists’, The Guardian, 4 December 2008 (Randeson, J.), Copyright Guardian News & Media Ltd 2008.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 5
• Be aware of the difference between sensation and perception.
• Describe the processes involved in sensation, such as
• Describe each of the sense organs and how they function. • Think of reasons why such senses have evolved.
transduction and sensory coding.
QUESTIONS TO THINK ABOUT
• Is the importance of a sense reflected in the amount of brain capacity needed to support it?
• How many senses do we have? • Why are some animals more reliant on some senses than • Why did the senses evolve? others? Are some senses more important to us than others? • • Are there some stimuli that we sense, even though we are not consciously aware of sensing them? • Which sense do we use least (or think we do) and why? • Do the different senses function along similar lines, using • How can we tell the difference between the sight (and similar mechanisms?
sound) of a bird and a plane, or between the smell of chocolate and gas? Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activites on: Normal vision, nearsightedness, farsightedness • Perceiving sound • The olfactory system • Manipulating your sense of smell • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
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Sensation and behaviour Our senses are the means by which we experience the world; everything we learn is detected by sense organs and transmitted to our brains by sensory nerves. Without sensory input, a human brain would be utterly useless; it would learn nothing, think no thoughts, have no experiences and control no behaviours. Vision, to most people, is the most important sense modality. Through it we recognise family and friends, see their facial expressions and gestures, learn to read, perceive objects that are beyond our reach, and find our way around our environment. It provides us with information about the size, shape, colour and movement of objects nearby and at a distance. Through vision, we receive some of our most powerful aesthetic experiences, in the form of art, a sexual partner and other beautiful images. The other senses also contribute to the richness of experience. Because of the role that speech plays in human culture, audition is important for social behaviour and communication. Audition and vision provide information about distant events, as does the sense of smell, which can tell us about sources of aromatic molecules before we can see or hear that source. The other senses deal with immediate and proximal events such as the taste of our favourite food or the touch of someone we love. The body senses are closely tied to our own movements. When we feel an object, the experience is active, not passive; we move our hands over it to determine its shape, texture and temperature. And information from specialised organs in the inner ear and from receptors in the muscles and joints is generated by our own movements. This information helps us to maintain our balance as we engage in our everyday activities.
Sensory processing Experience is traditionally divided into two classes: sensation and perception. Most psychologists define sensation as the detection of simple properties of stimuli, such as brightness, colour, warmth and sweetness. Perception is the detection of objects (both animate and inanimate), their locations, their movements and their backgrounds. According to these definitions, seeing the colour red is a sensation, but seeing a red apple is a perception. Similarly, seeing a movement is a sensation, but seeing a cricket ball coming towards us and realising that we will have to move to the left to catch it is a perception. Psychologists used to believe that perceptions depended heavily on learning whereas pure sensations involved
innate, ‘prewired’ physiological mechanisms. However, neither behavioural nor physiological research has been able to establish a clear boundary between ‘simple’ sensations and ‘complex’ perceptions. Research indicates that experience is essential to the development of some of the most elementary features of sensory systems (Blakemore and Mitchell, 1973). This is called ‘functional validation’ – the notion whereby the nervous system needs to be stimulated during development in order for it to develop properly. According to tradition, we have five senses: vision (seeing), audition (hearing), gustation (tasting), olfaction (smelling) and somatosensation (touching). In fact, we have several more. The somatosensory system, for example, includes separate components that are able to detect touch, warmth, coolness, vibration, physical damage (pain), head tilt, head movement, limb movement, muscular contraction and various events occurring within our bodies (Kandel et al., 1995). Whether we choose to call each of these components ‘senses’ is a matter of terminology.
Transduction Sense organs detect the presence of environmental stimuli provided by light, sound, odour, taste or mechanical contact. This information is transmitted to the brain through neural impulses – action potentials carried by the axons in sensory nerves. The task of the sense organs is to transmit signals to the brain that are coded in such a way as to faithfully represent the events that have occurred in the environment. The task of the brain is to analyse this information and reconstruct what has occurred. Transduction (literally, ‘leading across’) is the process by which the sense organs convert energy from environmental events into neural activity. Each sense organ responds to a particular form of energy given off by an environmental stimulus and translates that energy into neural firing to which the brain can respond. The means of transduction are as diverse as the kinds of stimuli we can perceive. In most senses, specialised neurons called receptor cells release chemical transmitter substances that stimulate other neurons, thus altering the rate of firing of their axons. In the somatosenses (‘body senses’), dendrites of neurons respond directly to physical stimuli without the intervention of specialised receptor cells. However, some of these neurons do have specialised endings that enable them to respond to particular kinds of sensory information. Table 5.1 summarises the types of transduction accomplished by our sense organs.
Sensory coding As you saw in Chapter 4, nerves are bundles of axons which can do no more than transmit action potentials. These action potentials are fixed in size and duration; they
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Table 5.1 The types of transduction accomplished by the sense organs Location of sense organ
Environmental stimuli
Energy transduced
Eye Ear Vestibular system Tongue Nose Skin, internal organs
Light Sound Tilt and rotation of head Taste Odour Touch Temperature Vibration Pain Stretch
Radiant energy Mechanical energy Mechanical energy Recognition of molecular shape Recognition of molecular shape Mechanical energy Thermal energy Mechanical energy Chemical reaction Mechanical energy
Muscle
cannot be altered. Thus, different stimuli cannot be translated into different types of action potential. Yet we can detect an enormous number of different stimuli with each of our sense organs. For example, we are capable of discriminating among approximately 7.5 million different colours. We can also recognise touches to different parts of the body, and we can further discriminate the degree of pressure involved and the sharpness or bluntness, softness or hardness, and the temperature of the object touching us. We can detect over 10,000 different odours. If action potentials cannot be altered, how do the sense organs tell the brain that a red apple or a yellow lemon has been seen or that the right hand is holding a small, cold object or a large, warm one? The answer is that the information from the sense organs must be coded in the activity of axons carrying information from the sense organs to the brain. A code is a system of symbols or signals representing information. Spoken English, written French, semaphore signals, magnetic fields on a recording tape, and the electrical zeros and ones in the memory of a computer are all examples of codes. As long as we know the rules of a code, we can convert a message from one medium to another without losing any information. Although we do not know the precise rules by which the sensory systems transmit information to the brain, we do know that they take two general forms: anatomical coding and temporal coding.
the location and type of sensory stimulus according to which incoming nerve fibres are active. For example, if you rub your eyes, you will mechanically stimulate the lightsensitive receptors located there. This stimulation produces action potentials in the axons of the nerves that connect the eyes with the brain (the optic nerves). The visual system of the brain has no way of knowing that the lightsensitive receptors of the eyes have been activated by an unnatural stimulus. As a result, the brain acts as if the neural activity in the optic nerves was produced by light – so you see stars and flashes. Experiments performed during surgery have shown that artificial stimulation of the nerves that convey taste produces a sensation of taste, electrical stimulation of the auditory nerve produces a sensation of a buzzing noise, and so forth (Calvin and Ojemann, 1994). Forms of anatomical coding distinguish not only between the sense modalities themselves, but also between stimuli of the same sense modality. Sensory coding for the body surface is anatomical: different nerve fibres serve different parts of the skin. Thus, we can easily discriminate between a touch on the arm and a touch on the knee. As you saw in Chapter 4, the primary somatosensory cortex contains a neural map of the skin. Receptors in the skin in different parts of the body send information to different parts of the primary somatosensory cortex. Similarly, the primary visual cortex maintains a map of the visual field.
Anatomical coding
Temporal coding
Since the early 1800s, when Johannes Müller formulated his doctrine of specific nerve energies (discussed in Chapter 1), we have known that the brain learns what is happening through the activity of specific sets of neurons. Sensory organs located in different places in the body send their information to the brain through different nerves. Because the brain has no direct information about the physical energy impinging on a given sense organ, it uses anatomical coding to interpret
Temporal coding is the coding of information in terms of time. The simplest form of temporal code is rate. By firing at a faster or slower rate according to the intensity of a stimulus, an axon can communicate quantitative information to the brain. For example, a light touch to the skin can be encoded by a low rate of firing, and a more forceful touch by a high rate. Thus, the firing of a particular set of neurons (an anatomical code) tells where the body is being touched; the rate at which these neu-
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rons fire (a temporal code) tells how intense that touch is. As far as we know, all sensory systems use rate of firing to encode the intensity of stimulation.
1. Experimenter sets the brightness of these lights to be equal
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2. Experimenter gradually changes the brightness of this light until the subject says the lights look different
Psychophysics is the systematic study of the relation between the physical characteristics of stimuli yp and the sensations they produce (the ‘physics of sych the mind’). To study perceptual phenomena, scientists had to find reliable ways to measure people’s sensations. Two of these methods are the just-noticeable difference and the procedures of signal detection theory. ee
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Figure 5.1 The method for determining a just-noticeable difference.
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Ernst Weber (1795–1878), a German anatomist and physiologist, investigated the ability of humans to discriminate between various stimuli. He measured the just-noticeable difference (jnd) – the smallest change in the magnitude of a stimulus that a person can detect. He discovered a principle that held true for all sensory systems: the jnd is directly related to the magnitude of that stimulus. For example, when he presented subjects with two metal objects and asked them to say whether they differed in weight, the subjects reported that the two weights felt the same unless they differed by a factor of 1 in 40. That is, a person could just barely distinguish a 40 g weight from a 41 g weight, an 80 g weight from an 82 g weight, or a 400 g weight from a 410 g weight. Psychologically, the difference between a 40 g weight and a 41 g weight is equivalent to the difference between an 80 g weight and an 82 g weight: 1 jnd. Different senses had different ratios. For example, the ratio for detecting differences in the brightness of white light is approximately 1 in 60. These ratios are called Weber fractions. Gustav Fechner (1801–87), another German physiologist, used Weber’s concept of the just-noticeable difference to measure people’s sensations. Assuming that the jnd was the basic unit of a sensory experience, he measured the absolute magnitude of a sensation in jnds. Imagine that we want to measure the strength of a person’s sensation of light of a particular intensity. We seat the subject in a darkened room facing two discs of frosted glass, each having a light bulb behind it; the brightness of the light bulb is adjustable. One of the discs serves as the sample stimulus, the other as the comparison stimulus, as seen in Figure 5.1. We start with the sample stimulus and the comparison stimulus turned off completely and increase the brightness of the comparison stimulus until our subject can just
detect a difference. That value is 1 jnd. Then we set the sample stimulus to that intensity (1 jnd) and again increase the brightness of the comparison stimulus just until our subject can again tell them apart. The new value of the comparison stimulus is 2 jnds. We continue making these measurements until our stimuli are as bright as we can make them or until they become uncomfortably bright for our subject. Finally, we construct a graph indicating the strength of a sensation of brightness (in jnds) in relation to the intensity of a stimulus. See Figure 5.2.
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Figure 5.2 A hypothetical range of perceived brightness (in jnds) as a function of intensity.
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Light did flash
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Source: J. Silver/SuperStock.
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Figure 5.3 According to signal detection theory, we must discriminate between the signal, conveying information, and noise, contributed by background stimuli and random activity of our own nervous systems.
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An alternative method of measuring a person’s sensitivity to changes in physical stimuli takes account of random changes in the nervous system (Green activit ee and Swets, 1974). According to signal detection theory, every stimulus event requires yp sych discrimination between signal (stimulus) and noise (consisting of both background stimuli and random activity of the nervous system). An example of this might involve an individual seated in a quiet room, facing a small warning light. The experimenter informs the individual that when the light flashes, he or she hears a faint tone one second later. The person’s task is to say yes or no after each flash of the warning light, according to whether or not they hear the tone. At first, the task is easy: some flashes are followed by an easily heard tone; others are followed by silence. As the experiment progresses, however, the tone gets fainter and fainter, until it is so soft that the individual has doubts about how to respond. The light flashes but did the individual really hear a tone or was it just imagined? Response bias – which, as you read about in Chapter 2, is the tendency to say yes or no when unsure of detecting a stimulus and can have a considerable effect on signal detection. According to the terminology of signal detection theory, hits are saying ‘yes’ when the stimulus is presented; misses are saying ‘no’ when it is presented; correct rejections are saying ‘no’ when the stimulus is not presented; and false alarms are saying ‘yes’ when the stimulus is not presented. Hits and correct rejections are correct responses; misses and false alarms are incorrect responses. Figure 5.4 shows the relationship between these responses. If a person wants to ensure that they are correct when they say yes (because they would feel foolish saying they have m
perceiving and perceiving. The just-noticeable difference can also be called a difference threshold, the minimum detectable difference between two stimuli. An absolute threshold is the minimum value of a stimulus that can be detected, that is, discriminated from no stimulus at all. Thus, the first comparison in the experiment just described – using a dark disc as the sample stimulus – measured an absolute threshold. The subsequent comparisons measured difference thresholds. Even early psychophysicists realised that a threshold was not an absolutely fixed value. When an experimenter flashes a very dim light, a subject may report seeing it on some trials but not on others. By convention, the threshold is the point at which a subject detects the stimulus 50 per cent of the time. This definition is necessary because of the inherent variability of the activity in the nervous system. Even when they are not being stimulated, neurons are never absolutely still; they continue to fire. If a very weak stimulus occurs when neurons in the visual system happen to be quiet, the brain is likely to detect it. But if the neurons happen to be firing, the effects of the stimulus are likely to be lost in the ‘noise’. Work such as that involved in air traffic control illustrates this point, as seen in Figure 5.3. The worker must select only the most relevant information from a background of competing information.
Figure 5.4 Four possibilities in judging the presence or absence of a stimulus.
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not used. Instead, a stimulus is more or less detectable. The person decides whether a stimulus occurred, and the consequences of making hits or false alarms can bias this decision: for example, missing the sound of an alarm clock may be more important than missing a telephone
100 £1 for hits £1 for hits; 50p fine for false alarms
Percentage of hits
heard something that is not there), the response bias is to err in favour of making hits and avoiding false alarms, even at the risk of making misses. Alternatively, a response bias might be to err in favour of detecting all stimuli, even at the risk of making false alarms. This response bias can seriously affect an investigator’s estimate of the threshold of detection. A conservative person will appear to have a higher threshold than will someone who does not want to let a tone go by without saying yes. Therefore, signal detection theorists have developed a method of assessing people’s sensitivity, regardless of their initial response bias. They deliberately manipulate the response biases and observe the results of these manipulations on the people’s judgements. Imagine, for example, that you are a participant in an experiment and the experimenter promises you a sum of money every time you make a hit (correctly report hearing a tone), with no penalty for false alarms. You would undoubtedly tend to say yes on every trial, even if you were not sure you had heard the tone; after all, you have nothing to lose and everything to gain. In contrast, imagine that the experimenter announced that she would fine you the same amount of money every time you made a false alarm and would give you nothing for making hits. You would undoubtedly say no every time, because you would have everything to lose and nothing to gain: you would be extremely conservative in your judgements. Now consider your response bias under a number of intermediate conditions. If you receive money for every hit but are also fined half that amount for every miss, you will say yes whenever you are reasonably sure you heard the tone. If you receive a sum of money for every hit but are fined twice as much for each false alarm, you will be more conservative. But if you are sure you heard the tone, you will say yes. The graph in Figure 5.5 is a receiver operating characteristic (ROC) curve, named for its original use in research at the Bell Laboratories to measure the intelligibility of speech transmitted through a telephone system. The curve shows performance when the sound is difficult to detect. If the sound were louder, so that you rarely doubted whether you heard it, you would make almost every possible hit and very few false alarms. The few misses you made would be under the low pay-off condition, when you wanted to be absolutely certain you heard the tone. The few false alarms would occur when guessing did not matter because the fine for being wrong was low or non-existent. The difference between the two curves seen in Figure 5.6 demonstrates that the louder tone is easier to detect. Detectability is measured by the relative distances of the curves from a 45-degree line. The signal detection method is the best way to determine an individual’s sensitivity to the occurrence of a particular stimulus. Note that the concept of threshold is
£1 for hits; £1 fine for false alarms 50
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Figure 5.5 A receiver operating characteristic (ROC) curve. The percentage of hits and false alarms in judging the presence of a stimulus under several pay-off conditions.
100 Loud tone Soft tone
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Figure 5.6 Two ROC curves, obtained by presenting a more discriminable stimulus (orange curve) and a less discriminable stimulus (red curve).
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106.9 FM
Frequency = 106.9 MHz (106,900,000 cycles/s) One cycle = 1/106,900,000 s; wavelength = 9.82 ft
Figure 5.7 Wavelength versus vibration. Because the speed of light is constant, faster vibrations produce shorter wavelengths.
The wavelength of visible light is much shorter, ranging from 380 to 760 nanometres (a nanometre, nm, is one-billionth of a metre). When viewed by a human eye, different wavelengths of visible light have different colours: for instance, 380 nm light looks violet and 760 nm light looks red. All other radiant energy is invisible to our eyes. Ultraviolet radiation, X-rays and gamma rays have shorter wavelengths than visible light has, whereas infrared radiation, radar and radio waves have longer wavelengths. The entire range of wavelengths is known as the electromagnetic spectrum; the part our eyes can detect – the part we see as light – is referred to as the visible spectrum, as seen in Figure 5.8. The definition of the visible spectrum is based on the human visual system. Some other species of animals would define the visible spectrum differently. Bees, for example, can see ultraviolet radiation that is invisible to us. Some plants have taken advantage of this fact and produce flowers that contain dyes that reflect ultraviolet radiation, presenting patterns that attract bees to them. Some snakes (notably, pit vipers such as the rattlesnake) have special organs that detect infrared radiation. This ability enables them to find their prey in the dark by detecting the heat emitted by small mammals in the form of infrared radiation. activit
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The eye and its functions
The eyes are important and delicate sense yp sych organs – and they are well protected. Each eye is housed in a bony socket and can be covered by the eyelid to keep out dust and dirt. The eyelids are edged by m
The eye is sensitive to light. Light consists of radiant energy similar to radio waves. As the radiant energy is transmitted from its source, it oscillates. For example, the antenna that broadcasts the programmes of your favourite FM station may transmit radio waves that oscillate at 88.5 MHz (megahertz, or million times per second). Because radiant energy travels at 297,600 km/s, the waves transmitted by this antenna are approximately 3.3 m apart (297,600 km divided by 88.5 million equals approximately 3.3 m). Thus, the wavelength of the signal from the station – the distance between the waves of radiant energy – is 3.3 m (see Figure 5.7).
Speed of light = 186,000 miles/s Wavelength
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The visual system allows us to do many activities that we take for granted: in a quick glance we can recognise what there is to see – people, objects and landscapes – in depth and full colour. Because of the dominance of visual information in our lives, it is perhaps not surprising that vision is our dominant sense.
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call. Signal detection theory emphasises that sensory experience involves factors other than the activity of the sensory systems, such as motivation and prior experience. Sensitivity to a signal can be influenced by these factors. The fact that you know that you will either be rewarded or financially penalised for making false alarms will influence the care with which you make decisions. You can see signal detection theory applied in a number of important ways. For example, a radiologist who takes an X-ray has to discriminate between shadows on an X-ray image that indicate disease – the signal – and those that just show differences in the anatomy of the patient – the noise (Parasuraman, 1985). Response bias can occur if the radiologist knows whether the patient has a history of disease or not. The likelihood of detecting a tumour increases or decreases, respectively. There is a quasi-experiment reported in the literature of factory workers complaining about the weight of large boxes that they had to shift. Carrying these heavy boxes made their backs ache. All the boxes were black. The supervisor, for reasons that you can imagine, decided to replace the black boxes with lighter-coloured ones. When the workers returned to the factory after the weekend and had to move the new boxes, they remarked on how much lighter they were than the black boxes even though the new boxes weighed the same as the old boxes. Why do you think this was?
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Wavelength in nanometres 400
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Figure 5.8 The electromagnetic spectrum.
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eyelashes, which help keep foreign matter from falling into the open eye. The eyebrows prevent sweat on the forehead from dripping into the eyes. Reflex mechanisms provide additional protection: the sudden approach of an object towards the face or a touch on the surface of the eye causes automatic eyelid closure and withdrawal of the head. Figure 5.9 shows a cross-section of a human eye. The transparent cornea forms a bulge at the front of the eye and admits light. The rest of the eye is coated by a tough white membrane called the sclera (from the Greek skleros, ‘hard’). The iris consists of two bands of muscle that control the amount of light admitted into the eye. The brain controls these muscles and thus regulates the size of the pupil, constricting it in bright light and dilating it in dim light. The space immediately behind the cornea is filled with aqueous humour, which simply means ‘watery fluid’. This fluid is constantly produced by tissue behind the cornea that filters the fluid from the blood. In place of blood vessels, the aqueous humour nourishes the
Jelly-like substance that fills eye (upper half has been removed)
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Figure 5.9 A cross-section of the human eye.
cornea and other portions of the front of the eye; this fluid must circulate and be renewed. If aqueous humour is produced too quickly or if the passage that returns it to the blood becomes blocked, the pressure within the eye can increase and cause damage to vision – a disorder known as glaucoma. Because of its transparency, the cornea must be nourished in this unusual manner. Our vision would be less clear if we had a set of blood vessels across the front of our eyes. The curvature of the cornea and of the lens, which lies immediately behind the iris, causes images to be focused on the inner surface of the back of the eye. Although this image is upside-down and reversed from left to right, the brain interprets this information appropriately. The shape of the cornea is fixed, but the lens is flexible; a special set of muscles can alter its shape so that the eye can obtain focused images of either nearby or distant objects. This change in the shape of the lens to adjust for distance is called accommodation. Normally, the length of the eye matches the refractive power of the cornea and the lens so that the image of the visual scene is sharply focused on the retina. However, for some people these two factors are not matched, and the image on the retina is therefore out of focus. There is a problem with sensing objects at various distances: some have difficulty in focusing on objects in the distance; others have difficulty in focusing on near objects. These people need an extra lens in front of their eyes (in the form of spectacles or contact lenses) to correct the discrepancy and bring the image into focus. People whose eyes are too long (front to back) are said to be nearsighted; they need a concave lens to correct the focus. The image on the right of Figure 5.10 shows what a nearsighted person would see. People whose eyes are too short are said to be farsighted; they need a convex lens. As people get older, not only does the cornea of the eye begin to yellow and the sensitivity of the rods to decline (Sturr et al., 1997), but the lenses of their
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eyes also become less flexible and it becomes difficult for them to focus on objects close to them. These people need reading glasses with convex lenses (or varifocals, if they already wear glasses) (see Figure 5.11). The retina, which lines the inner surface of the back of the eye, performs the sensory functions of the eye. Embedded in the retina are over 130 million photorecep-
tors – specialised neurons that transduce light into neural activity. The information from the photoreceptors is transmitted to neurons that send axons towards one point at the back of the eye – the optic disc. All axons leave the eye at this point and join the optic nerve, which travels to the brain (see Figure 5.12).
Lens Iris Normal sight Cornea Image focused in front of fovea
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Figure 5.11 Lenses used to correct nearsightedness and farsightedness.
Convex lens corrects farsightedness
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Figure 5.10 To a nearsighted person, distant objects are blurry and out of focus.
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Figure 5.12 A view of the back of the eye. The photograph shows the retina, the optic disc and blood vessels. Source: Courtesy of Douglas G. Mollerstuen, New England Medical Center.
Because there are no photoreceptors directly in front of the optic disc, this portion of the retina is blind. If you have not located your own blind spot, try the demonstration shown in Figure 5.13. Before the seventeenth century, scientists thought that the lens sensed the presence of light. Johannes Kepler (1571–1630), the astronomer who discovered the true shape of the planets’ orbits around the sun, is credited with the suggestion that the retina, not the lens, contained the receptive tissue of the eye. It remained for Christoph Scheiner (another German astronomer) to demonstrate in 1625 that the lens is simply a focusing device. Scheiner obtained an ox’s eye from a slaughter-
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house. After carefully peeling the sclera away from the back of the eye, he was able to see an upside-down image of the world through the thin, translucent membrane that remained. As an astronomer, he was familiar with the fact that convex glass lenses could cast images, so he recognised the function of the lens of the eye. Figure 5.14 shows a cross-section of the retina. The retina has three principal layers. Light passes successively through the ganglion cell layer (front), the bipolar cell layer (middle) and the photoreceptor layer (back). Early anatomists were surprised to find the photoreceptors in the deepest layer of the retina. As you might expect, the cells that are located above the photoreceptors are transparent. Photoreceptors respond to light and pass the information on by means of a transmitter substance to the bipolar cells, the neurons with which they form synapses. Bipolar cells transmit this information to the ganglion cells, neurons whose axons travel across the retina and through the optic nerves. Thus, visual information passes through a three-cell chain to the brain: photoreceptor– bipolar; cell–ganglion; and cell–brain. A single photoreceptor responds only to light that reaches its immediate vicinity, but a ganglion cell can receive information from many different photoreceptors. The retina also contains neurons that interconnect both adjacent photoreceptors and adjacent ganglion cells. The existence of this neural circuitry indicates that some kinds of information processing are performed in the retina.
R = Rods C = Cones B = Bipolar cells A = Amacrine cells G = Ganglion cells H = Horizontal cells
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Figure 5.13 A test for the blind spot. With the left eye closed, look at the + with your right eye and move the page back and forth, towards and away from yourself. At about 20 cm, the coloured circle disappears from your vision because its image falls on your blind spot.
Figure 5.14 The cells of the retina. Source: Adapted from J.E. Dowling and B.B. Boycott (1996) Proceedings of the Royal Society of London, 166, 80–111.
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The human retina contains two general types of photoreceptors: 125 million rods and 6 million cones, so called because of their shapes. Rods function mainly in dim light; they are very sensitive to light. Cones function when the level of illumination is bright enough to see things clearly. They are also responsible for colour vision. The fovea, a small pit in the back of the retina approximately 1 mm in diameter, contains only cones and is responsible for our most detailed vision. When we look at a point in our visual field, we move our eyes so that the image of that point falls directly on the cone-packed fovea. Farther away from the fovea, the number of cones decreases and the number of rods increases. Up to 100 rods may converge on a single ganglion cell. A ganglion cell that receives information from so many rods is sensitive to very low levels of light. Rods are therefore responsible for our sensitivity to very dim light, but they provide poor acuity.
Transduction of light by photoreceptors Although light-sensitive sensory organs have evolved independently in a wide variety of animals – from insects to fish to mammals – the chemistry is in essence the same in all species: a molecule derived from vitamin A is the central ingredient in the transduction of the energy of light into neural activity (carrots are said to be good for vision because they contain a substance that the body easily converts to vitamin A). In the absence of light, this molecule is attached to another molecule, a protein. The two molecules together form a photopigment. The photoreceptors of the human eye contain four kinds of photopigment (one for rods and three for cones), but their basic mechanism is the same. When a photon (a particle of light) strikes a photopigment, the photopigment splits apart into its two constituent molecules. This event starts the process of transduction. The splitting of the photopigment causes a series of chemical reactions that stimulate the photoreceptor and cause it to send a message to the bipolar cell with which it forms a synapse. The bipolar cell sends a message to the ganglion cell, which then sends one on to the brain, as seen in Figure 5.15. Intact photopigments have a characteristic colour. Rhodopsin, the photopigment of rods, is pink (rhodon means ‘rose’ in Greek). However, once the photopigments are split apart by the action of light, they lose their colour – they become bleached. Franz Boll discovered this phenomenon in 1876 when he removed an eye from an animal and pointed it towards a window that opened out onto a brightly lit scene. He then examined the retina under dim light and found that the image of the scene was still there. The retina was pink where little light had fallen and pale where the image had been bright. It was Boll’s discovery that led investigators to suspect that a chemical reaction was responsible for the transduction of light into neural activity.
Bipolar cell
Ganglion cell
Photoreceptor
Photon strikes photopigment
Photopigment splits, chemical reactions produce message
Message is transmitted to bipolar cell
Message is transmitted to ganglion cell Message is sent to the brain
Figure 5.15 Transduction of light into neural activity. A photon strikes a photoreceptor and causes the photopigment to split apart. This event initiates the transmission of information to the brain.
After light has caused a molecule of photopigment to split and become bleached, energy from the photoreceptor’s metabolism causes the two molecules to recombine. The photopigment is then ready to be bleached by light again. Each photoreceptor contains many thousands of molecules of photopigment. The number of intact, unbleached molecules of photopigment in a given cell depends on the relative rates at which they are being split by light and being put back together by the cell’s energy. The brighter the light, the more bleached photopigment there is.
Adaptation to light and dark Think, for a moment, about how difficult it can be to find a seat in a darkened cinema. Another example: if you have just come in from the bright sun, your eyes do not respond well to the low level of illumination. However, after a few minutes, you can see rather well – your eyes have adapted to the dark. This phenomenon is called dark adaptation. In order for light to be detected, photons must split molecules of rhodopsin or one of the other photopigments. When high levels of illumination strike the retina, the rate of regeneration of rhodopsin falls behind the rate of the bleaching process. With only a small percentage of the rhodopsin molecules intact, the rods are not very sensitive to light. If you enter a dark room after being in a brightly lit room or in sunlight, there are too few intact rhodopsin molecules for your eyes to respond immediately to dim light. The probability that a photon will strike an intact molecule of rhodopsin is very low. However, after a while, the regeneration of rhodopsin overcomes the bleaching effects of the light energy. The rods become full of unbleached rhodopsin, and a photon passing through a rod is likely to find a target. The eye has become dark adapted.
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Eye movements Our eyes are never completely at rest, even when our gaze is fixed on a particular place called the fixation point. Our eyes make fast, aimless, jittering movements, similar to the fine tremors our hands and fingers make when we try to keep them still. They also make occasional slow movements away from the target they are fixed on, which are terminated by quick movements that bring the image of the fixation point back to the fovea. Although the small, jerky movements that the eyes make when at rest are random, they appear to serve a useful function. Riggs et al. (1953) devised a way to project stabilised images on the retina – images that remain in the same location on the retina. They mounted a small mirror in a contact lens worn by the participant and bounced a beam of light off it. They then projected the image onto a white screen in front of the participant, bounced it off several more mirrors, and finally directed it towards the participant’s eye, as illustrated by Figure 5.16. The path of the light was arranged so that the image on the screen moved in perfect synchrony with the eye movements. If the eye moved, so did the image; thus, the image that the experimenters projected always fell on precisely the same part of the retina despite the subject’s eye
Screen
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movements. Under these conditions, details of visual stimuli began to disappear. At first, the image was clear, but then a ‘fog’ drifted over the subject’s field of view, obscuring the image. After a while, some images could not be seen at all. All of this occurred within seconds. These results suggest that elements of the visual system are not responsive to an unchanging stimulus. The photoreceptors or the ganglion cells, or perhaps both, apparently cease to respond to a constant stimulus. The small, involuntary movements of our eyes keep the image moving and thus keep the visual system responsive to the details of the scene before us. Without these involuntary movements, our vision would become blurry soon after we fixed our gaze on a single point and our eyes became still. The eyes also make three types of ‘purposive’ movement: conjugate movements, saccadic movements and pursuit movements. Conjugate movements are cooperative movements that keep both eyes fixed on the same target, or, more precisely, that keep the image of the target object on corresponding parts of the two retinas. If you hold up a finger in front of your face, look at it, and then bring your finger closer to your face, your eyes will make conjugate movements towards your nose. If you then look at an object on the other side of the room, your eyes will rotate outward, and you will see two separate blurry images of your finger. As you will learn in Chapter 6, conjugate eye movements assist in the perception of distance. When you scan the scene in front of you, your gaze travels from point to point as you examine important or interesting features. As you do so, your eyes make jerky saccadic movements – you shift your gaze abruptly from one point to another. For example, when you read a line in this book, your eyes stop several times, moving quickly between each stop. You cannot consciously control the speed of movement between stops; during each saccade the eyes move as fast as they can. Much of the time, the scene in front of us contains moving objects: objects blown by the wind, cars, aeroplanes, animals, other people. When we concentrate on one of these objects, we fix our gaze on it and track its movements with our eyes. These tracking movements, which follow the object we are watching, are called pursuit movements.
Colour vision Contact lens Eye mirror
Figure 5.16 A procedure for stabilising an image on the retina. Source: Riggs, L.A., Ratliff, F., Cornsweet, J.C. and Cornsweet, T.N., Journal of the Optical Society of America, 1953, 43, 495–501.
Light consists of radiant energy having wavelengths between 380 and 760 nm. Light of different wavelengths gives rise to sensations of different colours. How can we tell the difference between different wavelengths of light? Experiments have shown that there are three types of cone in the human eye, each containing a different type of photopigment. Each type of photopigment is most sensitive to light of a particular wavelength. That is, light of a particular wavelength most readily causes a particular photo-
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yp Vision is a synthetic sensory modality. It synthesych sises (puts together) rather than analyses (takes apart). When two wavelengths of light are present, we see an intermediate colour rather than the two components. In contrast, the auditory system is analytical. If a high note and a low note are played together on a piano, we hear both notes instead of a single, intermediate tone. The addition of two or more lights of different wavelengths is called colour mixing. Colour mixing is an additive process and is very different from paint mixing. So are its results. If we pass a beam of white light through a prism, we break it into the spectrum of the different wavelengths it contains. If we recombine these colours by passing them through another prism, we obtain white light again (see Figure 5.18). Colour mixing must not be confused with pigment mixing – what we do when we mix paints. An object has a particular colour because it contains pigments that absorb some wavelengths of light (converting them into heat) and reflect other wavelengths. For example, the chlorophyll found in the leaves of plants absorbs less green light than light of other wavelengths. When a leaf is illuminated by white light, it reflects a high proportion of green light and appears green to us. h syc la
Decreasing saturation
Increasing saturation
Increasing brightness
Table 5.2 Physical and perceptual dimensions of colour Perceptual dimension
Physical dimension
Physical characteristics
Hue
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Intensity
Saturation
Purity
Frequency of oscillation of light radiation Amount of energy of light radiation Intensity of dominant wavelength relative to total radiant energy
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Most colours can be described in terms of three physical dimensions: wavelength, intensity and purity. Three perceptual dimensions – hue, brightness and saturation – corresponding to these physical dimensions describe what we see. The hue of most colours is determined by wavelength; for example, light having a wavelength of 540 nm is perceived as green. A colour’s brightness is determined by the intensity, or amount of energy, of the light that is being perceived, all other factors being equal. A colour of maximum brightness dazzles us with a lot of light. A colour of minimum brightness is simply black. The third perceptual dimension of colour, saturation, is roughly equivalent to purity. A fully saturated colour consists of light of only one wavelength, for example pure red or pure blue. Desaturated colours look pastel or washed out. See Table 5.2 for a summary of the dimensions of colour. Saturation is probably the most difficult dimension of colour to understand. White light consists of a mixture of all wavelengths of light. Although its components consist of light of all possible hues, we perceive it as being colourless. White light is completely desaturated; no single wavelength is dominant. If we begin with light of a single wavelength (a pure, completely saturated colour) and then mix in some white light, the result will be a less
Colour mixing
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The dimensions of colour
saturated colour. For example, when white light is added to red light (700 nm), the result is pink light. The dominant wavelength of 700 nm gives the colour a reddish hue, but the addition of white light to the mixture decreases the colour’s saturation. In other words, pink is a less saturated version of red. Figure 5.17 illustrates how a colour having a particular dominant wavelength (hue) can vary in its brightness and saturation.
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pigment to split. Thus, different types of cone are stimulated by different wavelengths of light. Information from the three types of cone enables us to perceive colours. Wavelength is related to colour, but the terms are not synonymous. For example, the spectral colours (the colours we see in a rainbow, which contains the entire spectrum of visible radiant energy) do not include all the colours that we can see, such as brown, pink, and the metallic colours silver and gold. The fact that not all colours are found in the spectrum means that differences in wavelength alone do not account for the differences in the colours we can perceive.
Decreasing brightness
Figure 5.17 Hue, brightness and saturation. The colours shown have the same dominant wavelength (hue) but different saturation and brightness.
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Figure 5.18 Colour mixing. White light can be split into a spectrum of colours with a prism and recombined through another prism.
When we mix paints, we are subtracting colours, not adding them. Mixing two paints yields a darker result. For example, adding blue paint to yellow paint yields green paint, which certainly looks darker than yellow. But mixing two beams of light of different wavelengths always yields a brighter colour. For example, when red and green light are shone together on a piece of white paper, we see yellow. In fact, we cannot tell a pure yellow light from a synthesised one made of the proper intensities of red and green light. To our eyes, both yellows appear identical. To reconstitute white light, we do not even have to recombine all the wavelengths in the spectrum. If we shine a blue light, a green light and a red light together on a sheet of white paper and properly adjust their intensities, the place where all three beams overlap will look perfectly white. A colour television or a computer display screen uses this system. When white appears on the screen, it actually consists of tiny dots of red, blue and green light (see Figure 5.19).
Colour-coding in the retina In 1802, Thomas Young, a British physicist and physician, noted that the human visual system can synthesise any colour from various amounts of almost any set of three
colours of different wavelengths. Young proposed a trichromatic theory (‘three colour’ theory) of colour vision. He hypothesised that the eye contains three types of colour receptor, each sensitive to a different hue, and that the brain synthesises colours by combining the information received by each type of receptor. He suggested that these receptors were sensitive to three of the colours that people perceive as ‘pure’: blue, green and red. Young’s suggestion was incorporated into a more elaborate theory of colour vision by Hermann von Helmholtz. (We’ll return to Young in the section on creativity in Chapter 11.) Experiments in recent years have shown that the cones in the human eye do contain three types of photopigment, each of which preferentially absorbs light of a particular wavelength: 420, 530 and 560 nm. Although these wavelengths actually correspond to blue-violet, green and yellow-green, most investigators refer to these receptors as blue, green and red cones. To simplify the discussion here, we will assume that the three types of cone respond to these three pure hues. Red and green cones are present in about equal proportions. There are far fewer blue cones. Several scientists after Young and Helmholtz devised theories that took account of the fact that people also perceive yellow as a psychologically pure hue. Late in the nineteenth century, Ewald Hering, a German physiologist,
Figure 5.19 Additive colour mixing and paint mixing. When blue, red and green light of the proper intensity are all shone together, the result is white light. When red, blue and yellow paints are mixed together, the result is a dark grey.
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noted that the four primary hues appeared to belong to pairs of opposing colours: red/green and yellow/blue. We can imagine a bluish green or a yellowish green, or a bluish red or a yellowish red. However, we cannot imagine a greenish red or a yellowish blue. Hering originally suggested that we cannot imagine these blends because there are two types of photoreceptor, one kind responding to green and red and the other kind responding to yellow and blue. Hering’s hypothesis about the nature of photoreceptors was wrong, but his principle describes the characteristics of the information the retinal ganglion cells send to the brain. Two types of ganglion cell encode colour vision: red/green cells and yellow/blue cells. Both types of ganglion cell fire at a steady rate when they are not stimulated. If a spot of red light shines on the retina, exci-
Red light stimulates ‘red’ cone
tation of the red cones causes the red/green ganglion cells to begin to fire at a high rate. Conversely, if a spot of green light shines on the retina, excitation of the green cones causes the red/green ganglion cells to begin to fire at a slow rate. Thus, the brain learns about the presence of red or green light by the increased or decreased rate of firing of axons attached to red/green ganglion cells. Similarly, yellow/blue ganglion cells are excited by yellow light and inhibited by blue light. Because red and green light, and yellow and blue light, have opposite effects on the rate of axon firing, this coding scheme is called an opponent process. Figure 5.20 provides a schematic explanation of the opponent-process coding that takes place in the retina. Stimulation of a red cone by red light excites the red/green ganglion cell, whereas stimulation of a green
Green light stimulates ‘green’ cone
Yellow light stimulates ‘red’ and ‘green’ cones equally
Cones
E
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Ganglion cells
Red/green ganglion cell is excited; signals red
Red/green ganglion cell is inhibited; signals green
Yellow/blue ganglion cell is excited; signals yellow Excitation and inhibition cancel each other; no change in signal
(a)
(b)
(c)
Figure 5.20 Colour coding in the retina. (a) Red light stimulating a ‘red’ cone, which causes excitation of a red/green ganglion cell. (b) Green light stimulating a ‘green’ cone, which causes inhibition of a red/green ganglion cell. (c) Yellow light stimulating ‘red’ and ‘green’ cones equally. The stimulation of ‘red’ and ‘green’ cones causes excitation of a yellow/blue ganglion cell. The arrows labelled E and I represent neural circuitry within the retina that translates excitation of a cone into excitation or inhibition of a ganglion cell, respectively. For clarity, only some of the circuits are shown.
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yp Approximately one in 12 men has some form sych of defective colour vision. These defects are sometimes called colour-blindness, but this term should probably be reserved for the very few people who cannot see any colour at all. Men are affected more than women because many of the genes for producing photopigments are located on the X chromosome. Because males have only one X chromosome (females have two), a defective gene there will always be expressed. There are many different types of defective colour vision. Some individuals are missing a photopigment and are called dichromats (and the condition is called dichromacy). These people use two primary colours for matching and confuse various colours, as you will see below. Other individuals, called anomalous trichromats (the condition is called anomalous trichromacy), have an altered – not missing – photopigment. These people account for the majority of men with colour defects although they probably do not realise they have a deficit because they may only show a slight loss of sensitivity for the reds, greens and blues, but generally good colour discrimination. Extreme cases, however, will show greater loss of sensitivity and poorer colour discrimination. In rare cases, some people may express more than three photopigments and should, theoretically, have an added h syc la
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Figure 5.21 demonstrates an interesting property of the visual system: the formation of a negative after-image. Stare at the cross in the centre of the image on the left for approximately 30 seconds. Then quickly look at the cross in the centre of the white rectangle to the right. You will have a fleeting experience of seeing the red and green colours of a radish – colours that are complementary, or opposite, to the ones on the left. Complementary items go together to make up a whole. In this context, complementary colours are those that make white (or shades of grey) when added together. The most important cause of negative after-images is adaptation in the rate of firing of retinal ganglion cells. When ganglion cells are excited or inhibited for a prolonged period of time, they later show a rebound effect,
Defects in colour vision
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Negative after-images
firing faster or slower than normal. For example, the green of the radish in Figure 5.21 inhibits some red/green ganglion cells. When this region of the retina is then stimulated with the neutral-coloured light reflected off the white rectangle, the red/green ganglion cells – no longer inhibited by the green light – fire faster than normal. Thus, we see a red after-image of the radish.
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cone by green light inhibits the red/green ganglion cell (Figure 5.20 (a) and (b)). If the photoreceptors are stimulated by yellow light, both the red and green cones are stimulated equally. Because of the neural circuitry between the photoreceptors and the ganglion cells, the result is that the yellow/blue ganglion cell is excited, signalling yellow (Figure 5.20 (c)). The retina contains red/green and yellow/blue ganglion cells because of the nature of the connections between the cones, bipolar cells and ganglion cells. The brain detects various colours by comparing the rates of firing of the axons in the optic nerve that signal red or green and yellow or blue. Now you can see why we cannot perceive a reddish green or a bluish yellow: an axon that signals red or green (or yellow or blue) can either increase or decrease its rate of firing. It cannot do both at the same time. A reddish green would have to be signalled by a ganglion cell firing slowly and rapidly at the same time, which is impossible.
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Figure 5.21 A negative after-image. Stare for approximately 30 seconds at the cross in the centre of the left figure; then quickly transfer your gaze to the cross in the centre of the right figure. You will see colours that are complementary to the originals.
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Psychology in action – Red light = danger? According to some anthropologists, the colour red is seen as a sign of dominance in non-human species. Of course, what applies in the animal kingdom does not necessarily apply to the human kingdom. A study from researchers at the University of Durham, UK, however, suggests that it might. In a novel study, the researchers examined the success and failure of sportsmen and women who wore red or blue costumes (Hill and Barton, 2005). In the 2004 Olympic Games, contestants in the combat sports, boxing, tae kwon do, GrecoRoman wrestling and freestyle wrestling, were randomly given either red or blue costumes to wear. When Hill and Barton (2005) analysed the win rate of contestants, those in red costumes won more fights than those in blue costumes. They then further extended this research by examining the win rate of players in the Euro 2004 international football competition. The performance of five teams that wore red was compared with the performance of the same teams when they wore a different colour. Again, the study’s finding was novel: the team won more often when wearing red shirts. According to the authors, ‘given the ubiquity of aggressive competition throughout human societies and history, our results suggest that the evolutionary psychology of colour is likely to be a fertile field for further investigation’. The effect of the colour red even seems to extend to cognitive test performance. Researchers exposed students to either the colour red, green or black before giving them a test. Participants who were exposed to red – even if participants were not consciously aware of it – performed less well on a test than did those who were not (Elliot et al., 2007). The effect was found even when a number was written in red ink at the top of a sheet of paper. When participants’ brain activation was examined, there was greater activation in the right side of the frontal lobe when seeing the colour red (a theory, described in Chapter 13, argues that the left and right front parts of the brain mediate different kinds of emotional experiences, positive and negative respectively). But some psychologists have questioned this influence of red, especially that seen in the sport studies. For example, it could be argued that the colour itself did not influence the chances of winning but that fact that red was more highly visible
dimension to their colour vision. A study of women with a phenotype expressing four photopigments found that this was the case: these people perceived more chromatic appearances than did male or female trichromats (Jameson et al., 2001). Two of the three colour defects described below involve the red/green system. People with these defects confuse red and green. Their primary colour sensations
in the sports studied (Rowe et al, 2005). Some have also questioned the bias of the referee. The colour might influence the perception of performance, regardless of actual performance. In an ingenious test of this hypothesis, Hagemann et al., (2008) asked 42 experience tae kwon do referees to watch a videotape of five different sparring competitions. The competitors’s heads and trunk were covered in red or blue material. When asked to award points to these competitors, the red ones were given 13 per cent more points (as previous research would predict). Then, and this is the ingenious twist, the experimenters electronically switched the colours of the competitors – the actual competitors remained the same, as did their performance, but the colour they wore changed. When this happened, the points awarded to the red competitors increased. Those who had been given the points in the previous study (and were now dressed in blue) were awarded fewer. These results, according to the authors, suggest ‘need a change to the rules (i.e., to forbid red sports attire) and support referees by providing electronic-decision making only’.
Does the colour of a team’s kit influence their success? Source: Chris Coleman/Manchester United
are yellow and blue; red and green both look yellowish. Figure 5.22 shows one of the figures from a commonly used test for defective colour vision. A person who confuses red and green will not be able to see the ‘5’. The most serious defect, called protanopia (literally, ‘first-colour defect’), appears to result from a lack of the photopigment for red cones. The fact that people with protanopia have relatively normal acuity suggests that
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The third form of colour defect, called tritanopia (‘third-colour defect’), involves the blue cones and is much rarer: it affects fewer than 1 in 10,000 people. Tritanopes see the world in greens and reds; to them, a clear blue sky is a bright green, and yellow looks pink. The faulty gene that causes tritanopia is not carried on a sex chromosome, therefore it is equally common in males and females. This defect appears to involve loss of blue cones, but because there are far fewer of these than of red and green cones to begin with, investigators have not yet determined whether the cones are missing or are filled with one of the other photopigments. Figure 5.22 A figure commonly used to test for defective colour vision. People with red/green colour blindness will fail to see the 5. Source: Courtesy of American Optical Corporation.
they have red cones but that these cones are filled with green photopigment (Boynton, 1979). If red cones were missing, almost half of the cones would be gone from the retina, and vision would be less acute. To a protanope, red looks much darker than green, and reds and oranges generally appear very dark because the red end of the spectrum cannot be seen. Around 1 per cent of men suffer from this defect. The second form of red/green defect, called deuteranopia (‘second-colour defect’), appears to result from the opposite kind of substitution: green cones are filled with red photopigment. Around 8 per cent of European men and 0.5 per cent of European women have the inherited colour defect, Daltonism (protanopia and deuteranopia) (Fletcher and Voke, 1985) and there is evidence of other culture-related differences in colour vision impairment although whether such differences are due to cultural or physiological differences is unclear (Davies et al., 1998). The topic of colour perception and the use of colour terms across cultures is discussed in more detail in the next chapter.
Synaesthesia There are some individuals who claim to be able to sense colours when hearing words (and there are others who claim that tastes elicit sensations of shapes). This phenomenon is called synaesthesia (from the Greek syn, meaning ‘union’ and aisthesis meaning ‘sensation’): a sensation in one modality produces an inexorable sensation in another (Harrison and Baron-Cohen, 1996). It affects about 1 in 100,000 and cases of ‘coloured hearing’ were reported as early as the nineteenth century (Galton, 1883). One very famous composer, Liszt, claimed synaesthetic ability, see Figure 5.23. The phenomenon seems to be reliable. Baron-Cohen et al. (1987) investigated the synaesthetic ability of a 78year-old woman (EP) who claimed to see colours when she heard words. Her responses were 100 per cent consistent at 10 weeks whereas an IQ-matched control was only 17 per cent consistent at two weeks. Another example, recently reported in the literature, is that of a 20-year old undergraduate who consistently experienced tastes when hearing words (Gendle, 2007). Beeli et al. (2005) report the case of a right-handed musician (ES) who, when she hears a musical interval, reports a taste sensation on her tongue that is always associated with that
Figure 5.23 Some people claim to ‘see’ colours when they hear specific musical notes. The composer Liszt was one such person. Source: Brash, S., Maranto, G., Murphy, W. and Walker, B. (1990) How Things Work: The brain. Virginia: Time-Life Books. © 1990 Time-Life Books.
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Taste experienced
Vision involves the perception of objects in three dimensions, at a variety of distances, and with a multitude of colours and textures. These complex stimuli may occur at a single point in time or over an extended period. They may also involve an unchanging scene or a rapidly changing one. The other senses analyse much simpler stimuli (such as an odour or a taste) or depend on time and stimulus change for the development of a complex perception. For example, to perceive a solid object in three dimensions by means of touch, we must manipulate it – turn it over in our hands or move our hands over its surface. The stimulus must change over time for a fully-fledged perception of form to emerge. The same is true for audition: we hear nothing meaningful in an instant. Most people consider the sense of hearing second in importance only to vision. In some ways it is more important. A blind person can converse and communicate with other people almost as well as a sighted person. Deafness is much more likely to produce social isolation. A deaf person cannot easily join in the conversation of a group of people who do not know sign language. Although our eyes can transmit much more information to the brain, our ears are used for some of our most important forms of social communication.
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Tone interval
Audition
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Table 5.3 The taste sensations in ES triggered by different notes
Synaesthesia highlights one of the problems of studying sensation. The problem is as old as psychology and philosophy: how do we really know that the person is experiencing what they say they are experiencing? BaronCohen’s studies suggest two ways of circumventing this problem: (1) look for consistency of responses in an experimental group over time and compare these with control responses, and (2) compare brain activation in these two groups, working under the assumption that synaesthesia activates different areas of the brain when compared with a resting state and with a non-synaesthete control group.
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specific interval. (The types of taste sensations evoked by the notes can be seen in Table 5.3). Baron-Cohen et al. (1993) studied nine individuals who claimed to sense colours when hearing speech. The participants were tested at two points, one year apart. The researchers found that identical responses were reported in 92.3 per cent of cases over one year. For a control group, the response rate was 37.6 per cent after only one week. Some colours were specifically elicited by vowels. For example, the same colours were consistently associated with ‘i’, ‘o’ and ‘u’ (88.9 per cent of the time). One hypothesis suggests that synaesthetes show a breakdown in modularity, that is, there are links between the colour and language regions that have either disappeared or never even existed in non-synaesthetes. In synaesthetes, however, these links are intact. Alternatively, non-synaesthetes can inhibit the activity of these modules but this inhibition is dysfunctional in synaesthetes. Paulesu et al. (1996) used PET technology to study six synaesthete women who were asked to indicate which colours they sensed when hearing words and tones. The experimenters found that synaesthesia was elicited by words but not by tones. While both synaesthetes and controls activated the perisylvian regions of the brain, the synaesthetes showed activation of other visual association areas including the posterior inferior temporal cortex and the junction between the parietal and occipital cortex. No activation was observed in the major visual areas such as the primary visual cortex (V1) suggesting that it is possible to experience conscious visual perception without activating V1. This lack of V1 activation suggests to the researchers that synaesthesia involves an interaction between the areas of the brain responsible for higher visual function and the areas responsible for aspects of language processing.
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Loudness
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Figure 5.24 The physical and perceptual dimensions of sound waves.
Sound waves are measured in frequency units of cycles per second called hertz (Hz). The human ear perceives vibrations between approximately 30 Hz and 20,000 Hz. Sound waves can vary in intensity and frequency. These variations produce corresponding changes in sensations of loudness and pitch. Consider a loudspeaker. Alternations in the electrical current transmitted from an amplifier cause the loudspeaker cone to move back and forth. If the cone begins vibrating more rapidly, the pitch of the sound increases. If the vibrations become more intense (that is, if the cone moves in and out over a greater distance), the loudness of the sound increases. A third perceptual dimension, timbre, corresponds to the complexity of the sound vibration. See Figure 5.24.
The ear and its functions ee
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When people refer to the ear, they usually mean what anatomists call the pinna – the flesh-covered yp sych cartilage attached to the side of the head (pinna means ‘wing’ in Latin). But the pinna performs only a small role in audition: it helps us to determine the direction of sound. The real business of hearing is done in the inner ear (see Figure 5.25). The eardrum is a thin, flexible membrane that vibrates back and forth in response to sound waves. It passes these vibrations, via the bones of the middle ear, to the inner ear, a 2 cm cavity which separates the outer and middle ear. The eardrum is attached to the first of three middle ear bones called the ossicles (literally, ‘little bones’). The three ossicles are known as the malleus, incus and stapes (from Latin: hammer, anvil and stirrup) because of their shapes. These bones act together, in lever fashion, to transmit the vibrations of the eardrum to the fluid-filled structure of the inner ear that contains the receptive organ. The part of the ear that contains the receptive organ of hearing is called the cochlea (kokhlos means ‘snail’, which also describes its shape). Uncoiled, this would reach 35 mm and is 2 mm in diameter (Goldstein, 2007). It is filled with
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liquid and a bony chamber attached to the cochlea (the vestibule) contains two openings, the oval window and the round window. The last of the three ossicles (the stapes) presses against a membrane behind an opening in the bone surrounding the cochlea called the oval window, thus transmitting sound waves into the liquid inside the cochlea, where it can reach the receptive organ of hearing. The cochlea is divided along its length into three cavities by the basilar membrane and Reissner’s membrane. The auditory receptor cells sit on the surface of the basilar membrane. As the footplate of the stapes presses back and forth against the membrane behind the oval window, pressure changes in the fluid above the basilar membrane cause the basilar membrane to vibrate up and down. Because the basilar membrane varies in width and flexibility along its length, different frequencies of sound cause different parts of the basilar membrane to vibrate. High-frequency sounds cause the end near the oval window to vibrate, medium-frequency sounds cause the middle to vibrate, and low-frequency sounds cause the tip to vibrate. Figure 5.26 shows a schematic drawing and the corresponding photographic image of the cochlea.
Hammer Anvil Stirrup
Ossicles (middle ear bones)
Oval window Auditory nerve Bone
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Ear canal Pinna
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Figure 5.25 Anatomy of the auditory system.
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Reissner’s membrane External Internal hair hair cells cells Tectorial membrane
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Figure 5.26 (a) A schematic image of the cochlea. (b) A photographic image of the cochlea. Source: Beatty, J., Principles of Behavioral Neuroscience. Madison: Wm C. Brown Communications, Inc. Reprinted with permission.
In order for the basilar membrane to vibrate freely, the fluid in the lower chamber of the cochlea must have somewhere to go. Free space is provided by the round window. When the basilar membrane flexes down, the displacement of the fluid causes the membrane behind the round window to bulge out. In turn, when the basilar membrane flexes up, the membrane behind the round window bulges in. Some people suffer from a middle ear disease that causes bone to grow over the round window. Because their basilar membrane cannot easily flex back and forth, these people have a severe hearing loss. However, their hearing can be restored by a surgical procedure called fenestration (‘window making’) in which a tiny hole is drilled in the bone where the round window should be. Sounds are detected by special neurons known as auditory hair cells, located on the basilar membrane. Auditory hair cells transduce mechanical energy caused by the flexing of the basilar membrane into neural activity. These cells possess hair-like protrusions called cilia (‘eyelashes’). The ends of the cilia are embedded in a fairly rigid shelf (the tectorial membrane) that hangs over the basilar membrane like a balcony. When sound vibrations cause the basilar membrane to flex back and forth, the cilia are stretched. This pull on the cilia is translated into neural activity (see Figure 5.27). The threshold for hearing in humans is 100 trillionth of a metre – we can detect a sound that is as little in strength as 100 picometres. See Figure 5.28, which compares the movement of a hair cell with the equivalent necessary to move 10 mm of the Eiffel Tower.
When a mechanical force is exerted on the cilia of the auditory hair cells, the electrical charge across their membrane is altered. The change in the electrical charge causes a transmitter substance to be released at a synapse between the auditory hair cell and the dendrite of a neuron of the auditory nerve. The release of the transmitter substance excites the neuron, which transmits messages through the auditory nerve to the brain.
Detecting and localising sounds in the environment As we saw, sounds can differ in loudness, pitch and timbre. They also have sources; they come from particular locations. How does the ear distinguish these characteristics? The ear’s ability to distinguish sounds by their timbre depends on its ability to distinguish loudness and pitch. Some common auditory stimuli and their loudness levels are presented in Figure 5.29.
Loudness and pitch Scientists have long debated how the auditory system represents pitch on the auditory nerve. Some think that pitch is represented by axons firing in synchrony with the vibrations of the basilar membrane. However, axons cannot fire rapidly enough to represent the high pitches that we can hear. A good, young ear can distinguish frequencies of more than 20,000 Hz, but axons cannot fire more than 1,000 times per second. Therefore, high-frequency sounds, at least, must be encoded in some other way.
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Hair cells
Tectorial membrane (vibrations exert stretch on cilia of hair cells)
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Cilia of hair cell
Axons of auditory nerve
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Bone
Slice Through Cochlea
Membrane surrounding cochlea
Figure 5.27 The transduction of sound vibrations in the auditory system.
As we saw, sounds of different frequency cause different parts of the basilar membrane to vibrate. Thus, sounds of different frequencies stimulate different groups of auditory hair cells located along the basilar membrane. So, the brain can be informed of the pitch of a sound by the activity of different sets of axons from the auditory nerve. When low-frequency sound waves reach the ear, the top of the basilar membrane vibrates, and auditory hair cells located in this region are activated. In contrast, high-frequency sounds activate auditory hair cells located at the base of the basilar membrane, near the oval window. Therefore, the brain can tell the frequency from the set of axons which is firing. Two kinds of evidence indicate that pitch is detected in this way. First, direct observation of the basilar membrane has shown that the region of maximum vibration depends on the frequency of the stimulating tone (von
Békésy, 1960). Van Békésy’s place theory of hearing argued that the frequency of a sound is indicated by the place along the organ of Corti where the firing of nerves is strongest. The vibration of the basilar membrane is a little like the snapping of a whip, creating a travelling wave. When electrodes are placed along the cochlea, a map of frequencies can be plotted out along the cochlea (this is called a tonotopic map). Frequencies are higher at the base and lower at the apex of the cochlea. Secondly, experiments have found that damage to specific regions of the basilar membrane causes loss of the ability to perceive specific frequencies. The discovery that some antibiotics damage hearing (for example, deafness is one of the possible side effects of an antibiotic used to treat tuberculosis) has helped auditory researchers to investigate the anatomical coding of pitch. Stebbins et al. (1969) administered an antibiotic to different groups of
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Source: Goldstein, E. B. (2007) Sensation and Perception (7th edn). California: Thompson.
Lo u
Figure 5.28 Comparison of the movement of the cillia of a hair cell with the Eiffel Tower.
were exposed to the antibiotic, the more of their hair cells were killed. Damage started at the end of the basilar membrane nearest the oval window and progressed towards the other end. The experimenters compared the various groups of animals and found that the hearing loss was proportional to the amount of damage to the hair cells. The loss began with the highest frequencies and progressed towards the lower frequencies. Thus, the hair cells nearest the oval window are responsible for detecting high-pitched sounds. Although different frequencies cause different regions of the basilar membrane to vibrate and therefore different axons from the auditory nerve to fire, there is also evidence that pitch information can be encoded in a different way. The basilar membrane vibrates in synchrony with the sound waves. Neurons that are stimulated by hair cells located there are able to fire in synchrony with these vibrations, thus firing at the same frequency as the sound. The brain times the intervals between these responses and thus detects the pitch. This process is an example of temporal coding. One piece of evidence that low frequencies are detected in this way comes from an experiment performed many years ago by Miller and Taylor (1948). These investigators used white noise as a stimulus. White noise consists of a random mixture of all the perceptible frequencies of sound – it sounds like the ‘sssh’ heard when an FM radio is tuned between stations. White noise stimulates all regions of the basilar membrane because it contains all frequencies of sound. Miller and Taylor presented participants with white noise that passed through a hole in a rotating disc. By spinning the disc at various speeds, the investigators could divide the noise into extremely brief pulses, which could be presented at various rates. Thus, a ‘pitch’ was artificially created by setting the pulse rate of the white noise. When the frequency of the pulsation was less than 250 Hz, the participants could accurately identify its pitch. However,
Sh ou tin g Tr ai n
animals for varying times. Next, they tested the animals’ ability to perceive tones of different frequencies. Afterwards, they removed the animals’ cochleas and examined them. They found that the longer the animals
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Figure 5.29 The average decibel level of some common (and uncommon) noises. Source: Payne, D.G. and Wenger, M., Cognitive Psychology, 1998, p. 75. © 1998 Houghton Mifflin Company. Used with permission.
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above 250 Hz, the perception of pitch disappeared. Because the white noise stimulated all parts of the basilar membrane, the sounds must have been detected by neurons that fired in synchrony with the pulsations. What about loudness? The axons of the cochlear nerve appear to inform the brain of the loudness of a stimulus by altering their rate of firing. More intense vibrations stimulate the auditory hair cells more intensely. This stimulation causes them to release more transmitter substance, which results in a higher rate of firing by the axons in the auditory nerve. The code is therefore similar to that used in other senses. However, there is a problem. If they fire more frequently with sound intensity, why does that not signal a higher pitch according to the temporal code described above? Obviously, they cannot signal both loudness and pitch by the same means. The answer is that loudness is signalled by the number of auditory hair cells that are active at a given time. A louder sound excites a larger number of hair cells.
Timbre You can easily distinguish between the sounds of a violin and a clarinet, even if they are playing tones of the same pitch and loudness. So, clearly, pitch and loudness are not the only characteristics of a sound. Sounds can vary greatly in complexity. They can start suddenly or gradually increase in loudness, be short or long, and seem thin and reedy or full and vibrant. The enormous variety of sounds that we can distinguish is in large part owing to an important characteristic of sound called timbre. The combining, or synthesis, of two or more simple tones, each consisting of a single frequency, can produce a complex tone. For example, an electronic synthesiser produces a mixture of sounds of different frequencies, each of which can be varied in amplitude (intensity). Thus, it can synthesise the complex sounds of a clarinet or violin or can assemble completely new sounds not produced by any other source. Conversely, complex sounds that have a regular sequence of waves can be reduced by means of analysis into several simple tones. We can tell a clarinet from another instrument because each instrument produces sounds consisting of a unique set of simple tones called overtones. Their frequencies are multiples of the fundamental frequency, or the basic pitch of the sound. Timbre is the distinctive combination of overtones with the fundamental frequency. The fundamental frequency causes one part of the basilar membrane to vibrate, while each of the overtones causes another portion to vibrate. During a complex sound many different portions of the basilar membrane are vibrating simultaneously. Thus, the ear
analyses a complex sound. Information about the fundamental frequency and each of the overtones is sent to the brain through the auditory nerve, and the person hears a complex tone having a particular timbre. When you consider that we can listen to an orchestra and identify several instruments playing simultaneously, you can appreciate the complexity of the analysis performed by the auditory system.
Locating the source of a sound When we hear an unexpected sound, we usually turn our heads quickly to face its source. Even newborn infants can make this response with reasonably good accuracy. And once our faces are oriented towards the source of the sound, we can detect changes in its location of as little as 1 degree. To do so, we make use of two qualities of sound: relative loudness and difference in arrival time. Relative loudness is the most effective means of perceiving the side from which a high-frequency sound comes. Low-frequency sounds can bend around a solid object but high-frequency sounds bounce off. Thus, objects, such as the human head, cast an ‘acoustic shadow’ (at least for high-frequency sounds), rather as opaque objects cast a shadow in the sunlight. The head reflects high-frequency sounds so that they are made louder to the ear nearer the source of the sound and less loud at the more distant ear which is in the acoustic shadow cast by the head. Thus, if a source on your right produces a high-frequency sound, your right ear will receive more intense stimulation than your left ear will. The brain uses this difference to calculate the location of the source of the sound. The second method involves detecting differences in the arrival time of sound pressure waves at each eardrum. This method works best for frequencies below approximately 1,500 Hz. A 1,000 Hz tone produces pressure waves approximately 0.3 m apart. Because the distance between a person’s eardrums is about half that, a source of 1,000 Hz sound located to one side of the head will cause one eardrum to be pushed in while the other eardrum is being pulled out. In contrast, if the source of the sound is directly in front of the listener, both eardrums will move in synchrony. Researchers have found that when the source of a sound is located to the side of the head, axons in the right and left auditory nerves will fire at different times. The brain is able to detect this disparity, which causes the sound to be perceived as being off to one side. In fact, the brain can detect differences in firing times of a fraction of a millisecond (ms, one-thousandth of a second). The easiest stimuli to locate are those that produce brief clicks, which cause brief bursts of neural activity. Apparently, it
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is easiest for the brain to compare the arrival times of single bursts of incoming information. Each of these cues, the difference in the loudness and the difference in the timing across the ears, allows one to discriminate between left and right. However, humans are also able to tell whether sounds come from in front or behind, above or below. This information cannot be encoded by differences across the ears. This is where the role of the pinna (mentioned above) comes to the fore. The pinna has a very distinctive shape and for humans its usefulness is far from obvious from its appearance – contrast the obvious funnel shape of a horse’s ears which has plainly evolved to gather sound from a particular direction. The various ridges and folds of the human ear cause sound to interact with the surface in a process called acoustic interference. The result is that the timbre of the sound changes according to the sound direction. The importance of the pinna’s corrugations in sound localisation can be demonstrated by filling up the folds with plastic material and showing that localisation becomes much poorer.
The interaction between audition and vision The brain can also be ‘persuaded’ to believe that sounds can enhance the perception of visual stimuli. How senses interact is important because in real life we usually do not experience stimuli in only one sensory modality. In one study, eight observers watched a single flash, which was accompanied by multiple auditory beeps, spaced 57 ms apart (Shams et al., 2000). In this condition, observers reported having seen several flashes and not the one actually presented. Multiple flashes were consistently seen when multiple beeps were presented. When beeps were presented over 70 ms apart, however, the illusion was diminished and observers reported seeing single flashes. When a single beep was presented with multiple flashes, observers correctly reported seeing multiple flashes. The
study highlights how manipulable our senses can be: in this case, simply increasing the number of presentations of stimuli in one modality (vision) while presenting single instances of a stimulus in another modality (audition) made people believe they had been presented with more stimuli in the second of these senses than they had. A similar study explored the phenomenon whereby the introduction of a sound at the point when two identical visual targets pass ‘through’ each other leads people to report that they thought the two stimuli collided (Watanabe and Shimojo, 2001). Without the sound, people reported that the stimuli just seemed to stream through each other. Watanabe and Shimojo found that this collision effect could be weakened under certain conditions. For example, when identical auditory stimuli were presented 300 ms before and after the visual targets passed through each other, the collision effect did not occur. However, when the preceding and following sounds were different from the target sound, the collision effect remained. The context and the salience of the target sound, therefore, was important to preserving the effect. The effect may exist because when two real objects collide they usually make a transient sound. The inclusion of the target noise in these experiments seemed to provide the ‘missing’ sound that you would expect to hear when two objects collided. But if a target noise is preceded or followed by a similar noise, it will be difficult for the viewer/listener to draw a cause-and-effect relationship between the contact of the two images and the simultaneous noise because the simultaneous noise is the same as that which preceded and followed the collision.
Audition and the temporal cortex The cortical areas which mediate our perception of sound are located in the temporal cortex. One of the key features of the visual system is that it is organised hierarchically at the neural level. That is, sensory input is broken down and
Cutting edge – Hearing voices We know that when we hear our own voice on some recording device, it sounds different. We also seem to orient towards our own name, more than that of others – the cocktail party effect described later in Chapter 9. A group of researchers at the Institute for the Study of Child Development in New Jersey has recently reported that the brain regions activated when we hear our own name are different to those activated when we hear the names of others (Carmody and Lewis, 2006). They scanned four right-handed
young men, using fMRI, and found that areas of the left hemisphere – middle frontal cortex and middle and superior temporal cortex – were more active when the men heard their own names than others. The researchers note that these regions are also those which become active when people make judgements about themselves or their personal qualities, suggesting that they have a role in mediating our perception of ourselves and of stimuli personally relevant to us as individuals.
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then put together to form complex stimuli in various regions of the brain. This means that different regions of neurons are responsible for processing different types of visual stimuli. A similar phenomenon has also been demonstrated for the auditory sense: tones, non-speech stimuli, meaningless speech sounds and other types of auditory stimuli have been found to generate specific areas of the cortex (as well as areas they seem to have in common). For example, a recent study investigated whether certain types of stimuli activated ‘core’ auditory areas or a ‘belt’ region outside this core area (Wessinger et al., 2001). In an fMRI study, Wessinger et al., presented pure tones and complex auditory stimuli to 12 healthy, righthanded men and women. They found that pure tones activated a core area – areas that surrounded Heschl’s gyrus – but more complex stimuli activated areas outside this core (the pure tones did not). The authors propose that this hierarchical system of sound analysis participates in the early processing of many sounds including those for speech. Perry et al. (1999) found greater right-sided activation in the temporal cortex (the primary auditory cortex) when people sang than when they passively listened to singing. This region may be responsible for the processing of complex pitches. In an ingenious experiment, Halpern and Zatorre (1999) asked people to imagine the rest of a musical excerpt (the theme to the television series Dallas) after being cued with the first few notes. Blood flow was measured while participants imagined the piece of music. In the recruiting session, and prior to the scanning, the tune was played in order to familiarise participants with it. During scanning, the first five notes were played and participants were asked to imagine the rest of the sequence. When people imagined the rest of the tune, the right auditory association cortex and supplementary motor area were activated, suggesting that these regions are recruited in the imagination of meaningful complex auditory stimuli. Pantev et al. (1998) also found that musical training increased activation in those parts of the cortex involved in musical processing. In piano players who had played from age 12 to 28 years there was 25 per cent more activation in this region than there was in non-players. The current view of the auditory cortex’s contribution to sound processing, therefore, sees it as a region that is made up of a core (comprising the auditory cortex and nearby areas) and a parabelt (Tramo, 2001; Zattore et al., 2002), both of which contribute the hierarchical processing of sound. The core area extracts and analyses information about the pitch of tones (Zatorre et al., 2002). The belt and the parabelt in the right hemisphere appear to be areas which detect changes in the duration of notes and in the patterns of music; the parabelt in both hemispheres may be involved in grouping sounds by metre (Tramo, 2001). An area beyond the auditory
cortex, the frontal cortex, may be involved in organising sounds in time and keeping them ‘in mind’. The where and what aspects of hearing have been likened to those for sight. That is, there are two streams in the brain that allow us to locate a sound and another to identify it (Kaas and Hackett, 1999). The what, or ventral, stream is found anterior to the core of the belt and extends to the prefrontal cortex. The where, or dorsal, stream is found in posterior areas and extends to the parietal lobe. See Figure 5.30. Neurons in the anterior belt area fire more actively when responding to the pattern of sounds but weakly when trying to locate them. This neurophysiological finding is supported by research on a double dissociation in two patients with brain injury. Patient ES, for example, can recognise sounds but the ability to localise is poor (Clarke et al., 2002), whereas another patient is poor at recognising but good at localising sound. Figure 5.31 shows their responses and the brain regions damaged. Given what you now know about the auditory system, how would you describe the physiological basis of listening to a favourite piece of music, from initial sensation to recognition?
Deafness Deafness profoundly affects a person’s ability to communicate with others but hearing difficulties disappear in the company of other deaf people because they can sign read; it is only in the company of people who have normal hearing that deafness hinders a person’s ability to communicate (Sachs, 1989). People who are postlingually deaf – people who become deaf late in life, after they have learned oral and written language – are unlikely to
Figure 5.30 Areas associated with what (yellow) and where (blue) auditory functions, as determined by brain imaging. Source: Goldstein, E. B. (2007) Sensation and Perception (7th edn). California: Thompson.
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learn sign language. (In this context, lingual, from the word for ‘tongue’, refers to the acquisition of spoken language.) Some prelingually deaf people – people who are born deaf or who become deaf during infancy – never learn sign language, primarily because they are ‘mainstreamed’ in community schools or attend a school for the deaf that teaches oral communication. A recent technological development, the cochlear implant, is an electronic device surgically implanted in the inner ear that can enable deaf people to hear. Over 120,000 people had received such implants (Moore and Shannon, 2009) and the procedure is very sucessful (Krueger et al., 2008). It is most useful for two groups: people who become deaf in adulthood and very young children who can produce speech more easily if the implant occurs before the age of five (Tye-Murray et al., 1995). Putting a cochlear implant in a young child means that the child’s early education will be committed to the oralist approach. Many deaf people, however, resent the implication that deafness is something that needs to be repaired, seeing themselves as different but not at all defec-
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Source: Goldstein, E.B. (2007) Sensation and Perception (7th edn). California: Thompson.
We have two senses specialised for detecting chemicals in our environment: taste and smell. Together, they are referred to as the chemosenses and the process by which they sense chemicals is called chemosensation. Taste, or gustation, is the simplest of the sense modalities. We can perceive four, possibly five, qualities of taste: sourness, sweetness, saltiness, bitterness and umami (which produces a savoury sensation, like monosodium glutamate). Taste is not the same as flavour; the flavour of a food includes its odour, texture, temperature, shape as well as its taste: these are called head factors. You have probably noticed that the flavours of foods are diminished when you have a head cold. This loss of flavour occurs not because your taste buds are ineffective (you can actually tell whether a food is sweet or salty) but because congestion with mucus makes it difficult for odour-laden air to reach your sense of smell receptors. Without their characteristic odours to serve as cues, onions taste much like apples (although apples do not make your eyes water).
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Figure 5.31 (a) Coloured areas indicate brain damage for J.G (left) and E.S. (right). (b) Performance on recognition test (green bar) and localisation test (red bar). The horizontal line indicates normal performance.
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tive. In very rare cases, individuals who have damage to the auditory cortex and should, therefore, be ‘cortically’ deaf, appear to show evidence of hearing. If you had a child who was born deaf, would you send your child to a school that taught sign language or to one that emphasised speaking and lip-reading? Why? Now imagine that you are deaf (or, if you are deaf, that you are hearing). Would your answer change?
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The purpose of the sense of taste appears to be to provide guidance or warning to the gastrointestinal system: it will reject tastes it does not like and will accept those it does. This benefits us by allowing us to avoid ingesting potentially harmful substances (most poisons, for example, tend to be very bitter). Our ability to taste depends on the tongue, mouth and the receptors in them. The tongue has a corrugated appearance, being marked by creases and bumps. The bumps are called papillae (from the Latin, meaning ‘nipple’). Each papilla contains a number of taste buds (in some cases as many as 200) (see Figure 5.32(a) and (b) for an illustration). A taste bud is a small organ that contains a number of receptor cells, each of which is shaped rather like a segment of an orange. The cells have hairlike projections
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called microvilli that protrude through the pore of the taste bud into the saliva that coats the tongue and fills the trenches of the papillae. Molecules of chemicals dissolved in the saliva stimulate the receptor cells, probably by interacting with special receptors on the microvilli that are similar to the postsynaptic receptors found on other neurons. The receptor cells form synapses with dendrites of neurons that send axons to the brain through three different cranial nerves, the vagus, cranial and facial nerves. Information is sent from the nerves to the medulla, then the thalamus and then the cortex, as Figure 5.33 shows. Figure 5.32 (a) The taste buds
Figure 5.32 (b) The tongue, showing the four different types of papillae Source: Goldstein, E.B. (2007) Sensation and Perception (7th edn) California: Thompson.
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GUSTATION Ventral posterior nucleus (thalamus)
Primary gustatory cortex
Taste area 1
Taste area 2
Secondary gustatory cortex
Figure 5.34 The brain seems to have two taste areas – a primary and a secondary – located near the frontal lobe.
Solitary nucleus
Vagus nerve
Oral cavity
Glossopharyngeal nerve
Tongue
Facial nerve
near the front of the brain in regions called the insula or frontal operculum and further back in part of the parietal cortex; the location of the secondary taste cortex is not as well documented but appears to be principally in the orbitofrontal cortex. This is where flavour is thought to be processed (see page 560 in Chapter 13 on flavour). Other brain structures, such as the amygdala, contain cells that are responsive to taste and these cells may be partly responsible for determining the hedonic quality of taste – whether the food is palatable. The amygdala forms part of an area which Small et al. (1997) describe as the anteromedial temporal lobe (AMTL). Patients who have had this removed or damaged report increased sensitivity to bitter tastes and an elevated ability to recognise, but not detect, citric acid. Small et al. (2001a) have proposed that this region may play an important role in perceiving the intensity of tastes, especially aversive taste. One reason for the increase in intensity, may be that the damage to the AMTL disinhibited cells in the cortex that are sensitive to taste concentration or palatability. In a recent experiment, participants who were hungry or sated were asked to taste sucrose, caffeine, saccharine and citric acid (Haase et al., 2009). Hungry people activated different brain regions from those activated in satisfied ones. (Specifically, the insula, thalamus and substantia nigra). The sated participants showed less activation in the hippocampus and an area near the prefrontal lobe.
Figure 5.33 The neural pathway from tongue to brain. Source: Pinel, P.J., Biopsychology, 5th edn. Published by Allyn & Bacon, Boston, MA. Copyright © Pearson Education. By permission of the publisher.
Taste and the cortex There also appear to be primary and secondary taste cortices in the brain, as Figure 5.34 illustrates (Rolls and Baylis, 1994). The primary taste (gustatory) area is found
The four or more qualities of taste The surface of the tongue was once thought to be differentially sensitive to taste. The tip was considered most sensitive to sweet and salty substances; the sides to sour substances; and the back of the tongue, the back of the throat, and the soft palate overhanging the back of the tongue to bitter substances, as Figure 5.35 illustrates.
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Figure 5.35 It is commonly thought that different parts of the tongue allow the experience of different tastes; the figure seen here, and in many other textbooks, is inaccurate. Source: Whitfield, P. and Stoddart, M., Pathways of Perception. New York: Torstar Books.
This description, however, is largely mythical: the tongue is not this taste-specific and more than one region can detect the same sensation. There is also evidence that there may exist a fifth taste sensation, umami first reported at the beginning of the 20th century. This is difficult to describe accurately but appears to reflect the sensation we get when ingesting monosodium glutamate or very savoury foods (such as Chinese meals). The physical properties of the molecules that we taste determine the nature of the taste sensations. Different molecules stimulate different types of receptor. For example, all substances that taste salty ionise (break into charged particles) when they dissolve. The most important salty substance is table salt – sodium chloride (NaCl). Other chlorides, such as lithium or potassium chloride, and some other salts, such as bromides or sulphates, are also salty in taste, but none tastes quite as salty as sodium chloride. This finding suggests that the specific function of salt-tasting receptors is to identify sodium chloride. Sodium plays a unique role in the regulation of our body fluid. If the body’s store of sodium falls, we cannot retain water and our blood volume will fall. The result can be heart failure. Loss of sodium stimulates a strong craving for the salty taste of sodium chloride. Both bitter and sweet substances seem to consist of large, non-ionising molecules. Scientists cannot predict, merely on the basis of shape, whether a molecule will taste bitter or sweet (or neither). Some molecules (such as saccharin) stimulate both sweet and bitter receptors; they taste sweet at the front of the tongue and bitter at the back of the palate and throat. Most likely, the function of the bitterness receptor is to avoid ingesting poisons. Many plants produce alkaloids that serve to protect them against being eaten by insects or browsing animals. Some of these alkaloids are poisonous to humans, and most of them taste bitter. In contrast, the sweetness receptor enables us to recognise the sugar content of fruits and other nutritive plant foods. When sweet-loving animals
gather and eat fruit, they tend to disperse the seeds and help propagate the plant; thus, the presence of sugar in the fruit is to the plant’s advantage as well. Most sour tastes are produced by acids, in particular, by the hydrogen ion (H+) contained in acid solutions. The sourness receptor probably serves as a warning device against substances that have undergone bacterial decomposition, most of which become acidic. People who have suffered head injury or experienced certain types of medical treatment, such as radiotherapy, sometimes experience disorders of taste. These can vary from complete loss of taste (ageusia), decreased sensitivity (hypogeusia) and distorted taste sensations, especially those for meats, eggs, fruits, coffee and carbonated drinks (dysgeusia). Patients with these symptoms, however, are rare; only around 1 per cent of patients are ageusic, for example. A common complaint among those who suffer from one of these disorders is the lack of enjoyment of food and a loss of appetite.
The development of taste preference Newborns seem to respond in a characteristic way to some tastes, especially if these tastes are strong. When babies are given a sweet stimulus to ingest, they typically lick their lips, suck and look relaxed; when given bitter substances, the corners of their mouths depress, they tighten their eyes, flatten their tongues and shake their heads. Many adults who experience unfamiliar, strong bitter tastes do the same. Sour substances tend to elicit similar responses to those elicited by bitter ones but in a more diminished way. The development of taste preference appears to be highly malleable. For example, if a newborn is given sweetened water at 6 months of age, it will prefer sweetened water a year later; those fed normally will not show this preference for sweetened water. A similar finding is found when the newborn’s diet contains additional salt
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(Beauchamp and Moran, 1982; Harris and Booth, 1987). This learned response is also illustrated by adults’ food preferences. Our liking for foods such as lima beans, coffee, whisky and chillies, for example, grows from late childhood; children tend to find these foods too bitter (or hot in the case of chillies) to ingest.
Olfaction The sense of smell – olfaction – is one of the most interesting and puzzling of the sense modalities. It is unlike other sense modalities in two important ways. First, it is the only sense whose receptors are directly exposed to the environment. Secondly, people have difficulty identifying even familiar odours (Engen, 1987) although they can describe their properties very well (such as how nice smelling they are or what they remind them of). Odours have a powerful ability to evoke memories and feelings, even many years after an event, although they do not appear to be more effective than stimuli in other sensory modalities at doing this (Herz and Cupchik, 1992; Herz and Engen, 1996). At some time in their lives, most people encounter an odour that they recognise as having some childhood association, even though they cannot identify it. One of the most widely quoted examples is the experience of the French novelist Marcel Proust, whose mammoth series of autobiographical adventures, À la recherche du temps perdu (Remembrance of Things Past), was provoked by the odour of a madeleine cake dipped in tea which transported him back to his childhood. It is also a sense which we think we can do without; if asked which of the senses is least important to us or which we would be willing to relinquish if we had to, people usually nominate the sense of smell (Martin et al., 2001). Olfaction, like audition, seems to be an analytical sense modality. That is, when humans sniff air that contains a mixture of familiar odours, we usually identify the individual components. The molecules do not blend together and produce a single odour in the same way that lights of different wavelengths produce a single colour. Other animals, such as dogs, have more sensitive olfactory systems than humans do because they have a great many more olfactory receptors (described below). The difference in sensitivity between our olfactory system and those of other mammals may be that other mammals put their noses where odours are the strongest – just above ground level. Even a bloodhound’s nose would not be very useful if it were located five feet above the ground, as ours is. You can see how effective a hound’s olfactory system is at tracking other animals from Figure 5.36. However, we should not underrate our own. We can
smell some substances at lower concentrations than can the most sensitive instruments (the human nose is actually more sensitive than a smoke detector) and a recent study has found that we can follow a 10 cm trail of chocolate essential oil in an open grass field while wearing a blindfold (Porter et al., 2007). This study also found that both nostrils were better than one at the task but, more specifically, that the velocity of air into the right nostril was 0.45 ms and in the left 0.3 ms. This gives a spatial reach of 1.5–2 cm in the left nostril and 1–1.5 cm in the right. There is also evidence of circadian asymmetry in sniffing. The velocity of inhalation is greater in one nostril than the other and the side changes throughout the day (Sobel et al., 1999). Odours interact with other senses in very peculiar ways. Djordjevic et al. (2004) asked participants to smell or imagine smelling the odours of either strawberry or ham as they took part in a taste detection task – the participants had to indicate at which point they detected the sweet taste of sucrose. People detected the taste of sucrose better when they smelled or imagined smelling strawberry than when they smelled/imagined smelling ham. The imagery of pleasant and unpleasant scents activates similar brain areas to those activated during the actual inhalation of those odours (Bensafi et al., 2007). People exposed to a pleasant odour they were not consciously aware of, have been found to rate photographs of neutral faces as more likeable (Li et al., 2007). The Cutting Edge section gives a more startling illustration.
Figure 5.36 Human’s path following a scent trial, as compared to a dog’s path. (a) Path of a dog following the scent trail of a pheasant dragged through a field (scent trail in yellow, dog’s path in red.) (b) Path of a human following a scent trail of chocolate essential oil through a field (scent trail in yellow, human’s path in red). Source: Reprinted by permission from MacMillan Publishers Ltd: Nature Neuroscience vol. 10. Nr 1, Jan 2007, copyright 2007 (r). Science Faction: Louie Psihoyos (L).
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Odours play an important role in the lives of most mammals. Although we do not make use of olfaction in identifying one another, we do use it to avoid some dangers, such as food that has spoiled, or gas. In fact, the odour of rotting meat will trigger withdrawal – a useful response if some of the rotten meat has been swallowed. Other animals recognise friends and enemies by means of
smell and use odours to attract mates and repel rivals. And the reproductive behaviour of laboratory mammals – and even the menstrual cycles of women – may be influenced by the odours emitted by other animals of the same species, a controversial topic taken up in the Controversies in Psychological Science section on p.200.
Cutting edge – Cheese, body odour and the orbitofrontal cortex Our sense of smell is one of the most manipulable. People can be convinced that a neutral odour has a scent and, when told that an odour has a particular quality, judge that odour accordingly (regardless of whether it has that quality). Researchers at Oxford University presented the odour of isovaleric acid (which has a cheesy odour) to 12 healthy young men and told them it was either ‘body odour’ or ‘cheddar cheese’ (de Araujo et al., 2005). Participant’s ratings of the odours’ pleasantness under each label condition, and their brain activation, was measured.
The odour was rated as significantly more unpleasant when labelled body odour than cheese, and activation in the anterior cingulate cortex and medial orbitofrontal cortex was greater when participants smelled clean air and the odour labelled cheese than body odour. The experiment demonstrates neatly how semantic information can influence hedonic judgement.
Odour perception – An international perspective Perfumery is a universal art and few of us have not received or bought a gift of scent or cologne, but do all cultures and nations respond to the same smells in the same way? As you might expect, the answer is no. In general, there are cross-cultural similarities in people’s responses to odour: there is a universal correlation between odour familiarity and pleasantness, for example. The more familiar a person thinks an odour is, the more likeable it is judged. A study of Japanese and German participants found that the number of memories evoked by pleasant and unpleasant odours was similar (Schleidt et al., 1988). But different cultures do rate the pleasantness of some odours differently. In one study, Haller et al. (1999) found that exposure to vanilla in childhood affected a German participant’s food preferences later in life (Germans, at one time, received bottled milk flavoured with vanilla). When German participants were asked to rate ketchup or ketchup scented with vanilla, those who had been bottle-fed preferred the vanilla ketchup, compared with those who were breast-fed. More directly, Doty et al. (1985) compared the ability of American Korean, Caucasian, African American and Japanese participants to identify odours on a brief scratch and sniff test called the University of Pennsylvania Smell Identification Test (the UPSIT). The Koreans were better at identification than
were the Caucasians and African Americans; the last two groups were better than the Japanese, probably because the US-validated odours were more familiar to the Westerners than to the Japanese. A study of odour detection thresholds (the lowest concentration at which a person can detect an odour) reported lower detection thresholds for Japanese ink and aniseed (Hübener et al., in press). Cultures also differ in the way they classify odour. For example, when Japanese and Sherpa people were asked to classify 20 artificial scents into perceptually similar categories, there was agreement on most but the Japanese classified some odours as ‘fishy’: Sherpa are not used to eating fish but the Japanese are famously fish-friendly (Ueno, 1993). Americans and French people are more likely to describe fruit odorants as sweets or flowers and flower odorants as cleaning products than are Vietnamese raters (Chrea et al., 2004). One comprehensive study asked a sample of Japanese and German participants to rate the pleasantness and ‘edibility’ of three classes of odours which the authors described as ‘European’, ‘Japanese’ and ‘International’ (Ayabe-Kanamura et al., 1998). Table 5.4 shows examples of each. Of the European odours, the Japanese sample rated the odours of church incense, anise and almond as less pleasant than did the
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Odour perception – Continued Table 5.4 The odorants used in Ayabe-Kanamura et al. (1998), together with participants’ descriptions of them Odorants
Descriptors
Japanese Dried bonito flakes Soy sauce Roasted tea Dried fermented soybeans India ink Japanese cypress wood flakes
dried fish soy sauce, soy Japanese tea fermented soybeans India ink wood, furniture
International Ground coffee Grated dark chocolate Chopped, roasted peanuts Lowenbrau Vick’s Vaporub Angel
coffee chocolate, cacao peanuts beer ointment with menthol perfume
European Marzipan Blue cheese Pernod Italian salami Sawdust of pinewood Catholic church incense
almond, marzipan cheese anise salami wood, furniture incense
Anatomy of the olfactory system activit
yo
n myp
b
m
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b
s
Figure 5.37 shows the anatomy of the olfactory system. The receptor cells for the olfactory yp system lie in the olfactory mucosa, one-inch sych square patches of mucous membrane located on the roof of the nasal sinuses, just under the base of the brain. The receptor cells have cilia that are embedded in the olfactory mucosa. They also have axons that pass through small holes in the bone above the olfactory mucosa and form synapses with neurons in the olfactory bulbs. The olfactory bulbs are stalk-like structures located at the base of the brain that contain neural circuits that perform the first analysis of olfactory information. There is evidence that the cortex also processes aspects of olfactory sensation and perception (Lorig, 1989; Small et al., 1997; Martin, 1998). For example, Martin (1998) recorded EEG from healthy individuals while they were exposed to a series of synthetic and real food odours. The odours included chocolate, spearmint, baked beans, strawberry, coffee and rotting ee
Germans, but rated the odour of cheese and pinewood as more pleasant. Of the international odours, the German sample rated perfume to be more pleasant and the odours of beer and peanuts to be less pleasant than did the Japanese. When asked whether the substance represented by an odour was edible, the Japanese rated the Japanese food odours to be more edible than did the Germans; the Germans found anise and almond to be more edible. The odours of cheese and peanuts were rated as more edible by the Japanese than the Germans. A coda, however. The sense of smell is notoriously duplicitous and deceitful – think of trying to put a name to a familiar or unfamiliar odour. It is difficult and is summed up by the term ‘tip-of-the-nose’ phenomenon. In the study above, 25 per cent of the Japanese sample thought that India ink represented an edible substance; 40 per cent of Germans thought that Vick’s Vaporub did.
pork. The odours of spearmint and chocolate (but primarily chocolate) were associated with significant reductions in one type of brain activity, theta (which we will consider at greater length in Chapter 9). Increases in this EEG waveband are thought to be associated with increased attention; it is plausible that the change in response to chocolate may reflect this pleasant odour’s ability to distract a person’s attention and make them feel relaxed. In a novel neuroimaging experiment, Small et al. (1997) compared neural activation while people smelled substances, tasted them or did both (that is, perceived flavour). In some conditions, the odours and the tastes did not match. Using soy sauce, water, coffee, grapefruit and strawberry as stimuli, the experimenters found that when the odours and tastes were presented simultaneously, there was a decrease in activation at the primary taste cortex and the primary and secondary olfactory cortex. When tastes and smells did not match, increases in the amygdala were found, suggesting a role for the amygdala in the processing of novel or unpleasant stimuli. (We return to this role of the amygdala in emotion in Chapter 13.)
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Myelin sheath To olfactory bulb Axons Olfactory receptor cell
Olfactory bulb
Olfactory mucosa
Supporting cell
Cilia of olfactory receptor cells
Tongue
Figure 5.37 The olfactory system.
The interaction between odour molecule and receptor appears to be similar to that of transmitter substance and postsynaptic receptor on a neuron. That is, when a molecule of an odorous substance fits a receptor molecule located on the cilia of a receptor cell, the cell becomes excited. This excitation is passed on to the brain by the axon of the receptor cell. Thus, similar mechanisms may detect the stimuli for taste and olfaction. However, the
mechanism for olfactory reception continues to be one of science’s mysteries. Unlike information from all other sensory modalities, olfactory information is not sent to the thalamus and then relayed to a specialised region of the cerebral cortex. Instead, olfactory information is sent directly to several regions of the limbic system, in particular to the amygdala and to the limbic cortex of the frontal lobe.
Controversies in Psychological Science – Do human pheromones exist? The issue Some species in the animal kingdom have a terrifically efficient sense of smell. Dogs have a remarkable ability to detect and discriminate between odours, hence their use in drugsniffing operations. The odour of vaginal copulins can arouse male monkeys. Scents which produce stereotypical responses in a receiving organism without the scent being overtly detected are called pheromones. A well-known example is androstenone (its full, chemical name is 5-alpha-16-androst16-en-3-one), a steroid developed in the testes of pigs which has a musk-like odour and is secreted in the saliva of male pigs during mating. The unusual feature of androstenone is that it can induce a sow to adopt the mating position when it is sprayed on her. Farmers and vets can even buy the chemical in aerosol form, Boarmate, so that the sow can be prepared for mating (Figure 5.38). (In fact, truffle hunters use sows to detect the delicacy because it contains androstenone.) Pigs are not the only
species to secrete androstenone. It is also present in men’s sweat glands and in the urine of men and women, although at stronger concentrations in men (Brooksbank et al., 1974). Does a human pheromone exist?
The evidence One of the earliest studies of the pheromone effect in humans was conducted by Martha McClintock in the 1970s (McClintock, 1971). She found that 17–22-year-old women students who lived and slept in the same halls of residence reported menstrual synchrony. That is, their menstrual cycles began on or about the same time. The effect was unrelated to food intake, lifestyle pattern or stress. The result is difficult to explain because no mechanism that we know of can account for the finding. McClintock suggested that the mechanism might be pheromonal or mediated by an awareness of another’s menstrual cycle. To explain the result, replications would be needed. If the effect was pheromonal then a controlled
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Controversies in Psychological Science – Continued
Source: National Geographic, September 1986; © Louie Psihoyos/ Science Faction.
experiment in which menstrual cycles were deliberately manipulated would show this. This is what Russell et al. (1980) did. They applied the sweaty secretions of a woman who had a history of 28-day cycles and experience of ‘driving’ (that is influencing) other women’s cycles, on the upper lips of 5 women, 3 times a week for 4 months. Six individuals wore odourless alcohol (the control group). The mean difference in cycle onset for the experimental group was 3–9 days before the experiment; 3–4 days during driving. Controls’ figures were 8 days and 9.2 days, respectively. A significant difference, therefore, was found between the experimental group’s cycle onset and that of controls. However, there were some important limitations to the study. The experiment was not single- or double-blind, which means (as you will recall from Chapter 2) that the experimenters knew which participant was in each condition and each participant knew the purpose of the experiment. The woman who provided the samples was also one of the experimenters. A similar experiment found that women reported shorter menstrual cycles when compounds from the follicular (late) stage of another woman’s cycle were placed on the upper lip; longer cycles were reported when receiving ovulatory compounds (Stern and McClintock, 1998). A group from the
M
Figure 5.38 Farmers and veterinary surgeons sometimes spray Boarmate onto a sow to get her to adopt the mating position (Boarmate contains a variant of the pheromone, andro stenone).
Monell Chemical Senses Center and Chicago University also found that chemical substances collected from lactating women increased the ‘sexual motivation’ of other women (such as sexual desire and fantasy) (Spencer et al., 2004). Women with partners experienced more sexual desire whereas women without partners experienced more sexual fantasies. Does this suggest that ‘pheromones’ can modulate ovulation? Or are the effects limited to healthy young women? Would the same effect occur in women on various types of oral contraceptive? And are there alternative explanations, other than pheromonal ones, for the results? Questions such as these crop up quite often in pheromone research in humans. They become even more pertinent when examining the results of studies investigating the effect of ‘pheromones’ on sexual attractiveness. The majority of experiments, for example, have tended to expose subjects to volatile chemicals in contexts which are not generally appropriate. For example, participants have rated imaginary verbal descriptions of people (Filsinger et al., 1984), pictures and slides of buildings, people and animals (Kirk-Smith and Booth, 1977; Kirk-Smith et al., 1978) or have indicated the number of sexual partners they have recently had (Filsinger and Monte, 1986). They have worn masks impregnated with an odour (Cowley et al., 1980), a necklace impregnated with the odour (Cowley and Brooksbank, 1991), worn the odour on the top lip (Benton, 1982), sat on a chair impregnated with the odour (Kirk-Smith and Booth, 1980; Pause, 2004), or used a doctored changing room cubicle (Gustavson et al., 1987). A recent study has even found that the presence of androstadienone increased the perception of pain (Villemure and Bushnell, 2007). As you can see, none of these conditions reflects the behaviour and contexts normally seen when physical attraction might occur. In the most ecologically valid experiment, Black and Biron (1982) required participants to interact with a confederate of the opposite sex who wore either androstenone or a control odour. The participant was later asked to rate the confederate for attractiveness. The experimenters found no effect of these chemicals on the rated attractiveness of the confederate. Another investigation examined the effect of male and female fragrances on women’s genital arousal during the follicular and periovulatory stages as participants watched a hardcore video or sexually fantasised (Graham et al., 2000). During the follicular stage only, genital arousal was greater during exposure to male fragrance when women were fantasising. One study found that exposure to 4, 16-androstadien-3-one made women feel more focused – although leaving other mood-related states unaffected (Lundstrom et al., 2003) while another found that fertile women were more sensitive to the odour of this chemical than the odour of rose, whereas the opposite was true of women using oral contraceptives (Lundstrom et al., 2006a).
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Controversies in Psychological Science – Continued When brain electrical activity in relation to this odour was measured in women, the brain responded more quickly to it than it did to control odours (Lundstrom et al., 2006b). There may be reasons for this beyond pheromonal ones: androstenone can be perceived as unpleasant (smelling like a gents’ lavatory) by some people and as a ‘chemical’ smell in those who can detect it but are not repulsed by it. Both reactions could have made the brain respond to this odour more quickly. Curiously, homosexual men, like heterosexual women, show increased activation in the hypothalamus when smelling 4, 16-androstadien-3-one (Savic et al., 2005). Common odours were found to activate similar areas in homosexual men and heterosexual men and women, suggesting that the response to the chemical can depend on sexual orientation more than sex. In a related study in which the body odour preferences of homosexual and heterosexual men and women was measured, researchers found that heterosexual men and women and lesbians preferred the body odour of homosexual men to
gay men; gay men preferred the body odour of gay men (Martins et al., 2005). None of the participants knew the sex or sexual orientation of the person who donated the body odour. All participants over 25, apart from gay men, preferred the body odour of lesbians to that of gay men. Gay men preferred the body odour of heterosexual women to that of heterosexual men. The results suggest that attraction to body odour can be sex- and sexual orientation- specific.
Conclusion There is some evidence that the organ in the brain responsible for detecting and acting on pheromones (the vomeronasal organ) may be absent in humans (Moran et al., 1995). If this organ is important for sensing pheromones then humans will have difficulty sensing pheromones. Meanwhile, however, the evidence suggests that if you want to attract a member of the opposite sex, a bottle of good perfume or cologne would be a better option than would exposing your armpits, or investing in a can of Boarmate.
The dimensions of odour
Fragrant Heliotrope Vanillin Vanilla Lavender Arnica Thyme Hops Bay Caraway Cloves Cassia Spicy
Ethereal
Burned
Cedarwood Eucalyptus Myrhh Myrtle Juniper Fennel Sassafras Marjoram Nutmeg Anise Pepper Ginger Cinnamon
Although we know that there are at least four qualities of taste and that a colour can be specified by hue, brightness and saturation, the several attempts at classifying odour have not been particularly successful. It seems to be a slippery sense to make sense of. One of the most famous systems, Henning’s odour prism (1916), seen in Figure 5.39, plotted different categories of odour qualities at six corners of a prism. Recent research in molecular biology suggests that the olfactory system uses up to 1,000 different receptor molecules, located in the membrane of the receptor cells, to detect different categories of odours (Jones and Reed, 1989; Buck and Axel, 1991; Axel, 1995). Linda Buck and Michael Axel won the Nobel Prize in 2004 for their discovery – that a family of genes was responsible for coding olfactory receptors. There are around 1000 different receptors in mice and around 350 in humans (Buck, 2004). Presumably, the presence of molecules of a substance with a particular odour produces a particular pattern of activity in the olfactory system. That is, the molecules will strongly stimulate some receptors, weakly stimulate others, and stimulate still others not at all. This pattern of stimulation is transmitted to the brain, where it is recognised as belonging to a particular odour. Malnic et al. (1999) found that some odorants generated weak firing at some receptors and strong firing at others, as the large and
Putrid
Orange oil Lemon oil Strawberry oil Pineapple oil Acetic ether Ethyl ether Acetone Turpentine Pine Canada balsam Spruce Mastic Frankincense Resinous
Figure 5.39 The odour prism proposed by Henning (1916). Source: from Goldstein. Sensation and Perception, International Edition, 7E. (c) 2007, Wadsworth, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions
small dots show in Figure 5.40 (a) and (b). It may be that different odorants are coded by different combinations of receptors so that one receptor could respond to more than one odorant. Researchers do not yet know exactly
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Olfactory Receptors 1
18
19
41
46
51
79
83
85
86 O
Octanoic acid
OH O
Nonanoic acid
OH
Octanol
OH
Bromohexanoic acid Bromooctanoic acid
BR
BR
O OH O OH
Figure 5.40 (a) Recognition profiles for some odorants. Large dots indicate that the odorant causes a high firing rate for the receptor listed along the top; small dots indicate lower firing rates for the receptor. The structure of the compounds are shown on the right. Source: Goldstein, E.B. (2007) Sensation and Perception (7th edn). California: Thompson.
out an fMRI study of the brain activation of eight righthanded men and eight right-handed women as they smelled pleasant, neutral and unpleasant odours (Yousem et al., 1999). Activation was greater in women, especially in the left and right frontal and perisylvian regions.
Figure 5.40 (b) The combination code for odour. The receptors that are shown in colour are the ones that respond to the odourant on the left. Notice that each odorant activates a different pattern of receptors, but that a given receptor responds to a number of different odorants. Source: from Goldstein. Sensation and Perception, International Edition, 7E. (c) 2007, Wadsworth, a part of Cengage Learning, Inc. Reproduced by permission. www.cengage.com/permissions
which molecules stimulate which receptors; nor do they know how the information from individual olfactory receptor cells is put together.
Sex differences Research suggests that women are, on average, better at identifying, recognising and detecting odours than are men (Doty et al., 1985) and give more positive and less negative hedonic emotional responses to some odours (Seubert et al., 2008). This sex difference may have important implications for any study of the neural basis of olfactory processing. If individual differences exist at the behavioural level (for example, detecting, recognising, identifying), then neural activation may be different in men and women when they both smell the same odours. To test this hypothesis, Yousem and his colleagues carried
The somatosenses The body senses, or somatosenses, include our ability to respond to touch, vibration, pain, warmth, coolness, limb position, muscle length and stretch, tilt of the head and changes in the speed of head rotation. The number of sense modalities represented in this list depends on one’s definition of a sense modality. However, it does not really matter whether we say that we respond to warmth and coolness by means of one sense modality or two different ones; the important thing is to understand how our bodies are able to detect changes in temperature. Many experiences require simultaneous stimulation of several different sense modalities. For example, taste and odour alone do not determine the flavour of spicy food; mild (or sometimes not-so-mild) stimulation of pain detectors in the mouth and throat gives Mexican food its special characteristic. Sensations such as tickle and itch are apparently mixtures of varying amounts of touch and pain. Similarly, our perception of the texture and threedimensional shape of an object that we touch involves cooperation among our senses of pressure, muscle and joint sensitivity, and motor control (to manipulate the object). If we handle an object and find that it moves smoothly in our hand, we conclude that it is slippery. If,
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after handling this object, our fingers subsequently slide across each other without much resistance, we perceive a feeling of oiliness. If we sense vibrations when we move our fingers over an object, it is rough. And so on. If you close your eyes as you manipulate some soft and hard, warm and cold, and smooth and rough objects, you can make yourself aware of the separate sensations that interact and give rise to a complex perception.
The skin senses The entire surface of the human body is innervated (supplied with nerve fibres) by the dendrites of neurons that transmit somatosensory information to the brain. Cranial nerves convey information from the face and front portion of the head (including the teeth and the inside of the mouth and throat); spinal nerves convey information from the rest of the body’s surface. All somatosensory information is detected by the dendrites of neurons; the system uses no separate receptor cells. However, some of these dendrites have specialised endings that modify the way they transduce energy into neural activity. Figure 5.41 shows the sensory receptors found in hairy skin and in smooth, hairless skin (such as skin on the palms of the hands or the soles of the feet). The most common type of skin sensory receptor is the free nerve ending, which resembles the fine roots of a plant. Free nerve endings infiltrate the middle layers of both smooth and hairy skin and surround the hair follicles in hairy skin. If you bend a single hair on your forearm, you will see how sensitive the free nerve endings are. The largest of the special receptive endings, called the Pacinian corpuscle, is visible to the naked eye. Pacinian corpuscles are very sensitive to touch. When they are moved, their axons fire a brief burst of impulses. Pacinian
Hairy Skin
Hair
Free nerve endings
Hairless Skin
Specialised receptor Sweat gland Pacinian corpuscle
Artery Vein
Figure 5.41 Sensory receptors in hairy skin (left) and in hairless skin (right).
corpuscles are thought to be the receptors that inform us about vibration. Other specialised receptors detect other sensory qualities, including warmth, coolness and pain.
Temperature There is general agreement that different sensory endings produce the sensations of warmth and coolness. Detectors for coolness appear to be located closer to the surface of the skin. If you suddenly place your foot under a stream of rather hot water, you may feel a brief sensation of cold just before you perceive that the water is really hot. This sensation probably results from shortlived stimulation of the coolness detectors located in the upper layers of the skin. Our temperature detectors respond best to changes in temperature. Within reasonable limits, the air temperature of our environment comes to feel ‘normal’. Temporary changes in temperature are perceived as warmth or coolness. Thus, our temperature detectors adapt to the temperature of our environment. This adaptation can be easily demonstrated. If you place one hand in a pail of hot water and the other in a pail of cold water, the intensity of the sensations of heat and cold will decrease after a few minutes. If you then plunge both hands into a bucket of water that is at room temperature, it will feel hot to the cold-adapted hand and cold to the hot-adapted hand. It is mainly the change in temperature that is signalled to the brain. Of course, there are limits to the process of adaptation. Extreme heat or cold will continue to feel hot or cold, however long we experience it.
Pressure Sensory psychologists speak of touch and pressure as two separate senses. They define touch as the sensation of very light contact of an object with the skin and pressure as the sensation produced by more forceful contact. Sensations of pressure occur only when the skin is actually moving, which means that the pressure detectors respond only while they are being bent. Just how the motion stimulates the neurons is not known. If you rest your forearm on a table and place a small weight on your skin, you will feel the pressure at first, but eventually you will feel nothing at all, if you keep your arm still. You fail to feel the pressure not because your brain ‘ignores’ incoming stimulation but because your sensory endings actually cease sending impulses to your brain. Studies that have measured the very slow, very minute movements of a weight sinking down into the skin have shown that sensations of pressure cease when the movements stop. With the addition of another weight on top of the first one, movement and sensations of pressure begin again (Nafe and Wagoner, 1941). A person will feel a
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very heavy weight indefinitely, but the sensation is probably one of pain rather than pressure. In terms of the perception of a person’s touch, we judge others’ skin to be more pleasant than our own and their forearms as smoother, softer and less sticky (Guest et al., 2009). Sensitivity to subtle differences in touch and pressure varies widely across the surface of the body. The most sensitive regions are the lips and the fingertips. The most common measure of the tactile discrimination of a region of skin is the two-point discrimination threshold. To determine this measure, an experimenter touches a person with one or both legs of a pair of dividers and asks the person to say whether the sensation is coming from one or two points. The further apart the legs of the dividers must be before the person reports feeling two separate sensations, the lower the sensitivity of that region of skin, as seen in Figure 5.42. Studies have also shown that the brain regions responsible for somatosensation may also be involved in the imagination of somatosensation. Data from neuroimaging studies of visual imagery and the imagination of movement, show that similar brain regions are activated during the actual perception of visual stimuli/the execution of an action and during the imagination of these visual stimuli/imagining making movements. You will find more on this phenomenon in the next chapter.
Pain Pain is a complex sensation involving not only intense sensory stimulation but also an emotional component. That is, a given sensory input to the brain might be interpreted as pain in one situation and as pleasure in another. For example, when people are sexually aroused, they become less sensitive to many forms of pain and may even find such intense stimulation pleasurable. Physiological evidence suggests that the sensation of pain is quite different from the emotional reaction to pain. Opiates such as morphine diminish the sensation of
Figure 5.42 The method for determining the two-point discrimination threshold.
pain by stimulating opioid receptors on neurons in the brain; these neurons block the transmission of pain information to the brain. In contrast, some tranquillisers (such as Valium) depress neural systems that are responsible for the emotional reaction to pain but do not diminish the intensity of the sensation. Thus, people who have received a drug like Valium will report that they feel the pain just as much as they did before but that it does not bother them much. Many noxious stimuli elicit two kinds of pain: an immediate sharp, or ‘bright’, pain followed by a deep, dull, sometimes throbbing, pain. Some stimuli elicit only one of these two kinds of pain. For example, a pinprick will produce only the superficial ‘bright’ pain, whereas a hard blow from a blunt object to a large muscle will produce only the deep, dull pain. Different sets of axons mediate these two types of pain. Pain – or the fear of pain – is one of the most effective motivators of human behaviour. However, it also serves us well in the normal course of living. As unpleasant as pain is, we would have difficulty surviving without it. For example, pain tells us if we have sprained an ankle, broken a bone or have an inflamed appendix. Neuroimaging studies have highlighted how the control of pain is related to different degrees of brain activation. Controlling this activation may reduce pain. For example, Koyama et al. (2005) administered thermal pain to 10 healthy volunteers as fMRI measured brain activation. As the pain became more intense, so did activation in the thalamus, prefrontal cortex and anterior cingulate cortex, areas of the brain known to respond to pain. When participants were told that they could expect a reduction in pain, however, there was a decrease in activation in these areas as well as a decrease in self-reported pain. Taking this finding a step further, deCharms et al. (2005) speculated on what might happen if activity in the anterior cingulate cortex (ACC) could be manipulated. If it could be reduced, would participants experience less pain? Hypnosis, for example, has been associated with reduced pain and, in turn, less activation in the ACC. The researchers studied 36 healthy volunteers, some of whom undertook a training course in increasing/decreasing brain activation and pain. These included instructions either to pay attention to the pain or to direct attention away from it; to perceive the stimulus as tissue-damaging, or as a neutral sensory stimulus; to perceive the stimulus as being either very or not very intense; and to control the experience or to be controlled by it. The pain stimulus was heat. When participants used these instructions to increase or decrease activation in the ACC, the perception of pain changed: those who were instructed to increase ACC activation, experienced more pain. When patients experiencing pain were given the same instructions, decreases in self-reported pain were found after training.
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The results suggest that when healthy people exposed to pain, and patients experiencing pain, follow instructions designed to reduce activation in a part of the brain known to respond during painful experiences, then such experiences are reduced.
Phantom limbs A particularly interesting form of pain sensation occurs after a limb has been amputated. After their limbs are gone, up to 70 per cent of amputees report that they feel as though their missing limbs still exist, and that they often hurt. This phenomenon is referred to as the phantom limb (Melzak, 1992). People who have phantom limbs report that the limbs feel very real, and they often say that if they try to reach out with their missing limbs, it feels as if they were responding. Sometimes, they perceive the limbs as sticking out, and they may feel compelled to avoid knocking them against the side of a door frame or sleeping in a position that would make the limbs come between them and the mattress. People have reported all sorts of sensations in phantom limbs, including pain, pressure, warmth, cold, wetness, itching, sweatiness and prickliness. The classic explanation for phantom limbs has been activity of the sensory axons belonging to the amputated limbs. Presumably, this activity is interpreted by the nervous system as coming from the missing limbs. When nerves are cut and connections cannot be re-established between the proximal and distal portions, the cut ends of the proximal portions form nodules known as neuromas. The treatment for phantom pain has been to cut the nerves above these neuromas, to cut the bundles of nerve fibres that bring the information from these nerves into the spinal cord, or to make lesions in somatosensory pathways in the spinal cord, thalamus or cerebral cortex. Sometimes these procedures work for a while, but, unfortunately, the pain often returns. Melzak (1992) suggests that the phantom limb sensation is inherent in the organisation of the parietal cortex. The parietal cortex is involved in our awareness of our own bodies. Indeed, people who have sensory neglect, caused by lesions of the right parietal lobe, have been known to push their own legs out of bed, believing that they actually belong to someone else. Melzak reports that some people who were born with missing limbs nevertheless experience phantom limb sensations, which would suggest that our brains are genetically programmed to provide sensations for all four limbs even if we do not have them.
The internal senses Sensory endings located in our internal organs, bones and joints, and muscles convey painful, neutral, and in some cases pleasurable sensory information. For example, the
internal senses convey the pain of arthritis, the perception of the location of our limbs, and the pleasure of a warm drink descending to our stomachs. Muscles contain special sensory endings. One class of receptors, located at the junction between muscles and the tendons that connect them to the bones, provides information about the amount of force the muscle is exerting. These receptors protect the body by inhibiting muscular contractions when they become too forceful. During competition, some weightlifters have received injections of a local anaesthetic near the tendons of some muscles to eliminate this protective mechanism. As a result, they are able to lift even heavier weights. Unfortunately, if they use this tactic, some tendons may snap or some bones may break. Another set of stretch detectors consists of spindleshaped receptors distributed throughout the muscle. These receptors, appropriately called muscle spindles, inform the brain about changes in muscle length. People are not conscious of the specific information provided by the muscle spindles, but the brain uses the information from these receptors and from joint receptors to keep track of the location of parts of the body and to control muscular contractions. Together these sensations are called proprioception – our sense of bodily position and movement – and the receptors for this sense, as the examples above show, are found in the joints of skeletons and skeletal muscles. Receptors at joints are called mechanoreceptors and these are essential for allowing us to sense the angle of a joint. There are four types of mechanoreceptors, most of which have specific functions such as responding to rapid movement of limbs or maintaining the position of limbs and so on. However, as studies of limb amputation and even hip replacements show, these receptors may take some time to adapt to changing bodily structure or function. People who have had hip replacement surgery, for example, can sense limb position, but they do not sense it very well. Unlike somatosensation, proprioceptive information seems to recruit different cortical regions so that data about tactile sensation are sent to specific areas of the somatosensory cortex and data from muscle afferents and from joints are sent to different ones. More complex proprioception and tactile sensation most probably involves posterior regions of the parietal lobes.
The vestibular senses What we call our ‘sense of balance’ involves several senses, not just one. If we stand on one foot and then close our eyes, we immediately realise how important a role vision plays in balance. The vestibular apparatus of the inner ear provides only part of the sensory input that helps us remain upright.
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The three semicircular canals, located in the inner ear and oriented at right angles to one another, detect changes in rotation of the head in any direction (see Figure 5.43). These canals contain a liquid. Rotation of the head makes the liquid flow, stimulating the receptor cells located in the canals. Another set of inner ear organs, the vestibular sacs, contain crystals of calcium carbonate that are embedded in a gelatin-like substance attached to receptive hair cells. In one sac, the receptive tissue is on the wall; in the other, it is on the floor. When the head tilts, the weight of the calcium carbonate crystals shifts, producing different forces on the cilia of the hair cells. These forces change the activity of the hair cells, and the information is transmitted to the brain. The vestibular sacs are very useful in maintaining an upright head position. They also participate in a reflex that enables us to see clearly even when the head is being jarred. When we walk, our eyes are jostled back and forth. The jarring of the head stimulates the vestibular sacs to cause reflex
Vestibular sacs
Nerves
Semicircular canals Cochlea
Semicircular canals
Figure 5.43 The three semicircular canals and two vestibular sacs located in the inner ear.
movements of the eyes that partially compensate for the head movements. People who lack this reflex because of localised brain damage must stop walking in order to see things clearly, for example to read a street sign.
Chapter review Sensory processing • We experience the world through our senses. Our knowledge of the world stems from the accumulation of sensory experience and subsequent learning. • All sensory experiences are the result of energy from events that is transduced into activity of receptors, which are specialised neurons. Transduction causes changes in the activity of axons of sensory nerves, and these changes in activity inform the sensory mechanisms of the brain about the environmental event. The information received from the receptors is transmitted to the brain by means of two coding schemes: anatomical coding and temporal coding. • In nineteenth-century Germany, Weber devised the concept of the just-noticeable difference (jnd), and Fechner used the jnd to measure the magnitude of sensations. • The methods of psychophysics apply to all sensory modalities, including sight, smell, taste, hearing and touch.
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Vision • The cornea and lens of the eyes cast an image of the scene on the retina, which contains photoreceptors: rods and cones. Cones gather visual information under illuminated conditions; rods work only when the light is very dim. • The energy from the light that reaches cones is transduced into neural activity when photons strike molecules of photopigment, splitting them into their two constituents. This
•
event causes the cones to send information through the bipolar cells to the ganglion cells. The axons of the ganglion cells travel through the optic nerves and form synapses with neurons in the brain. Vision requires the behaviour of looking, which consists of moving our eyes and head. Small, involuntary movements keep an image moving across the photoreceptors, thus preventing them from adapting to a constant stimulus. Saccadic eye movements are rapid ocular movements that are conjugate in nature; each eye is fixed on the same point. The focus of the lenses of the eyes is adjusted when looking from near to distant objects (and vice versa). When an image of the visual scene is cast upon the retina, each part of the image has a different colour, which can be specified in terms of its hue (dominant wavelength), brightness (intensity) and saturation (purity). Information about colour is encoded trichromatically by your cones; the red, green and blue cones respond in proportion to the amount of the appropriate wavelength contained in the light striking them. This information is transformed into an opponent-process coding, signalled by the firing rates of red/green and yellow/blue ganglion cells, and is transmitted to the brain. There are many different types of defective colour vision. Individuals missing a photopigment are called dichromats (and the condition is called dichromacy) and use two primary colours for matching and confuse various colours; anomalous
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trichromats (the condition is called anomalous trichromacy) have an altered – not missing – photopigment, and comprise the majority of men with colour defects; protanopia, the most serious condition, appears to result from a lack of the photopigment for red cones: red looks much darker than green, and reds and oranges generally appear very dark. • Synaesthesia refers to the phenomenon whereby a stimulus in one modality evokes a sensation in another.
Audition
Gustation and olfaction • Gustation and olfaction refer to the senses of taste and smell,
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• The physical dimensions of sound – amplitude, frequency and
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complexity – can be translated into the perceptual dimensions of loudness, pitch and timbre for sounds ranging from 30 Hz to 20,000 Hz. Sound pressure waves put the process in motion by setting up vibrations in the eardrum, which are passed on to the ossicles. Vibrations of the stirrup against the membrane behind the oval window create pressure changes in the fluid within the cochlea that cause the basilar membrane to flex back and forth. This vibration causes the auditory hair cells on the basilar membrane to move relative to the tectorial membrane. The resulting pull on the cilia of the hair cells stimulates them to secrete a transmitter substance that excites neurons of the auditory nerve. This process informs the brain of the presence of a sound. Two different methods of detection enable the brain to recognise the pitch of a sound. Different high-frequency and mediumfrequency sounds are perceived when different parts of the basilar membrane vibrate in response to these frequencies. Lowfrequency vibrations are detected when the tip of the basilar membrane vibrates in synchrony with the sound, which causes some axons in the auditory nerve to fire at the same frequency. Low-frequency sounds are located by differences in the arrival time of the sound waves in each ear. High-frequency sounds are located by differences in intensity caused by the ‘sound shadow’ cast by the head. The auditory system will analyse sounds of complex timbre into their constituent frequencies, each of which causes a particular part of the basilar membrane to vibrate. All these functions proceed automatically. The temporal lobe contains the primary auditory cortex and is active during the comprehension of the phonological aspects of language tasks, and when listening to music.
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respectively, and are called chemical senses. Both are served by cells having receptors that respond selectively to various kinds of molecule. We can perceive sweet, salty, sour or bitter tastes and a fifth, umami (which delivers a savoury sensation). To most organisms, sweet and moderately salty substances taste pleasant, whereas sour or bitter substances taste unpleasant. Sweetness and saltiness receptors permit us to detect nutritious foods and sodium chloride. Sourness and bitterness receptors help us avoid substances that might be poisonous. Olfactory information combines with information about taste to provide us with the flavour of a food present in our mouths. We can distinguish countless different odours and can recognise smells encountered in childhood. Women tend to be better detectors of odours than men. Unlike visual stimuli, odours do not easily blend. The detection of different odours appears to be accomplished by up to 1,000 different receptor molecules located in the membrane of the olfactory receptor cells. Pheromones are chemicals produced by the body which generate a stereotypical behavioural or physiological response without necessarily being detected. The evidence for human pheromones is weak, probably because humans lack the vomeronasal organ necessary to respond to such stimuli.
The somatosenses • The somatosenses gather several different kinds of information from different parts of the body.
• The skin senses of temperature, touch and pressure, vibration
• • •
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and pain inform us about the nature of objects that come in contact with our skin. Pacinian corpuscles in fingers can detect vibration caused by movement which helps us to determine the texture of surfaces. Temperature receptors detect hot and cold; free nerve endings can give rise to sensations of pain. Sensory receptors in muscles and joints inform the brain of the movement and location of arms and legs. This is called proprioception. The vestibular senses help an organism to keep balance.
Suggestions for further reading Sensation – general reading Coren, S., Ward, L.M. and Enns, J.T. (2003) Sensation and perception (6th edn). Chichester: Wiley. Goldstein, E.B. (2004) Blackwell Handbook of Sensation and Perception. Oxford: Blackwell.
Goldstein, E.B. (2007) Sensation and Perception. (7th edn). California: Thompson. Levine, M.W. and Shefner, J.M. (2000) Fundamentals of Sensation and Perception. Oxford: Oxford University Press. Schiffman, H.R. (2000) Sensation and Perception: An integrated approach (5th edn). Chichester: Wiley.
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Scientific American, 2006, 16, 3. Some excellent texts on sensation – and the Goldstein (2007) book is one of the very best on the subject. The special issue of the magazine focuses on the senses and includes excellent articles on the relationship between vision and consciousness, visual microchips, music and the brain, phantom limbs, how the blind draw, the chemistry of smell, and making sense of taste.
Vision Bruce, V., Green, P. and Georgeson, M. (2003) Visual Perception: Physiology, psychology and ecology (4th edn). Hove: Psychology Press. Gregory, R.L. (1998) Eye and Brain: The psychology of seeing (5th edn). New York: Oxford University Press. Zeki, S. (1993) A Vision of the Brain. Oxford: Blackwell Scientific. These three texts provide an excellent introduction to visual perception. Bruce et al.’s book is a good, solid undergraduate textbook covering most aspects of vision. Gregory’s and Zeki’s books provide a neurophysiological account of vision: these are exemplary texts of their kind and you should try to consult these.
There are many excellent books on hearing. These two are recommended for their thoroughness and accuracy. The Zatorre et al. article is a good review of the role of the cortex in the processing of sound.
Sensory interaction Kayser, C. (2007) Listening with your eyes. Scientific American Mind, 18, 2, 24–29. A nice article on the interaction between audition and vision.
Somatosensation Romo, R. and Salinas, E. (2001) Touch and go: Decision-making mechanisms in somatosensation. Annual Review of Neuroscience, 24, 107–37. Dobbs, D. (2007) The pain gate. Scientific American Mind, 18, 2, 48–55. A detailed but informative review of somatosensation and a provocative article on how a rare disorder can shed some light on how we experience pain.
Olfaction and gustation Audition King, A.J. and Nelken, I. (2009) Unravelling the principles of auditory cortical processing. Nature Neuroscience, 12, 698–701 Moore, D.R. and Shannon, R.V. (2009) Beyond cochlear implants. Nature Neuroscience, 12, 6, 686–691 Schnupp, J.W.H. and Carr, C.E. (2009) On hearing with more than one ear. Nature Neuroscience, 12, 692–697. Yost, W.A. (1994) Fundamentals of Hearing: An introduction (3rd edn). San Diego: Academic Press. Zattore, R.J., Berlin, P. and Penhune, V.B. (2002) Structure and function of auditory cortex: Music and speech. Trends in Cognitive Sciences, 6, 1, 37–46.
Doty, R.L. (2003) Handbook of Olfaction and Gustation (2nd edn). New York: Dekker. Martin, G.N. (2004) A neuro-anatomy of flavour. Petits Propos Culinaires, 76, 58–82. Smith, D.V. and Margolskee, R.F. (2001) Making sense of taste. Scientific American Mind, March, 26–33. Doty’s edited book covers a broad range of topics related to olfaction and gustation, with a particularly good introductory chapter. The article by Smith and Margolskee provides a very good review of our current understanding of the sense of taste. Martin’s article is a good review of the neuro-anatomy of smell and taste.
Journals to consult Brain
Perception
Chemical Senses
Perception and Psychophysics
Journal of Experimental Psychology: Human perception and performance
Psychological Science
Journal of Neuroscience
Science
Nature
Trends in Neurosciences
Neuroreport
Vision Research
Pain
Quarterly Journal of Experimental Psychology
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Website addresses http://psych.hanover.edu/Krantz/sen_tut.html A range of sensation and perception demonstrations. http://krantzj.hanover.edu/classes/Sensation/ John Krantz’s page on sensation. http://ear.berkeley.edu/~ear/ The University of Berkeley’s Hearing Sciences web pages; they include demonstrations and links. http://www.biols.susx.ac.uk/home/Chris_Darwin/Perception/Lecture _Notes/Hearing_Index.html A large course on auditory perception from the University of Sussex.
http://www.cbn-atl.org/edu_resources/classroom_activities/ senses/somatosensation.pdf A very nice web page illustrating various aspects of somatosensation. http://online.sfsu.edu/~swilson/emerging/artre325.smelltaste.html A large collection of gustation and olfaction links.
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In 1988, police raided the home of Cherry Groce, searching for her son, Michael, who was suspected of a robbery at a building society. A police officer shot Mrs Groce in the raid and the incident attracted considerable publicity. Subsequently, the son was apprehended and prosecuted for the robbery, a prosecution based entirely on the evidence of a CCTV (closed circuit television) image which showed a young black man, alleged to be Groce. One witness for the prosecution claimed that he was able to prove that the identities matched by comparing the precise numbers of pixels (the elements which make up a picture) separating key features of the face. Now this was impressive technical stuff for a jury, until the defence called an expert in facial movement. Alf Linney, a medical physicist from University College London, pointed out that if any of his students had committed such elementary mistakes in face comparison and measurement (not correcting for viewpoint and resolution), they would certainly fail. Michael Groce was acquitted. Source: Bruce, 1998, p. 332.
Explore the accompanying videos, simulations, and animations on MyPsychLab. This chapter includes activities on: Facial perception • Recognising the sex of a face • Cues to depth • The phi phenomenon • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available.
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 6
• Define perception. • Describe and understand how form, motion and space might be perceived.
• Describe the way in which the brain processes different types of visual information.
QUESTIONS TO THINK ABOUT
• How do we assemble sensory cues from the environment and turn them into something meaningful?
• What is it about a face that makes it recognisable? • How can we perceive a moving object as moving? • How can we tell a moving car from a moving bus or train?
• Describe and understand the way in which we recognise faces and other types of stimuli.
• Understand the consequences of brain damage on visual perception and be aware of how these might help us to understand how the brain normally perceives.
• Damage to which parts of the brain do you think would impair perception?
• Does the brain process different types of perception – form, space, motion, colour – differently?
• Are there stimulus-specific brain regions, ones that respond to specific classes of stimuli but not to others?
CHAPTER 6
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The nature of perception Take a look around you – around the room or out the window. What do you see as you and your eyes move around? Shapes? Figures? Background? Shadows? Areas of light and dark? Your knowledge of the objects you see and their relative location is extensive, and you have a good idea of what they will feel like, even if you have not touched them. If the lighting suddenly changes (if lamps are turned on or off or if a cloud passes in front of the sun), the amount of light reflected by the objects in the scene changes too, but your perception of the objects remains the same – you see them as having the same shape, colour and texture as before. Similarly, you do not perceive an object as increasing in size as you approach it, even though the image it casts upon your retina does get larger. Form, movement and space are the essential elements of perception. The brain receives fragments of information from approximately 1 million axons in each of the optic nerves. It combines and organises these fragments into the perception of a scene – objects having different forms, colours and textures, residing at different locations in three-dimensional space. Even when our bodies or our eyes move, exposing the photoreceptors to entirely new patterns of visual information, our perception of the scene before us does not change. We see a stable world, not a moving one, because the brain keeps track of our own movements and those of our eyes and compensates for the constantly changing patterns of neural firing that these movements cause.
Definition of perception Perception is the process by which we recognise what is represented by the information provided by our sense organs. This process gives unity and coherence to this input. Perception is a rapid, automatic, unconscious process; it is not a deliberate one in which we puzzle out the meaning of what we see. We do not first see an object and then perceive it; we simply perceive the object. Occasionally we do see something ambiguous and must reflect about what it might be or gather further evidence to determine what it is, but this situation is more problem-solving than perception. If we look at a scene carefully, we can describe the elementary sensations that are present, but we do not become aware of the elements before we perceive the objects and the background of which they are a part. Our awareness of the process of visual perception comes only after it is com-
plete; we are presented with a finished product, not the details of the process. The distinction between sensation and perception is not easy to make; in some respects, the distinction is arbitrary. Probably because of the importance we give to vision and because of the richness of the information provided by our visual system, psychologists make a more explicit distinction between visual sensation and perception than they do for any other sensory system.
Perception of form When we look at the world, we do not see patches of colours and shades of brightness. We see things – cars, streets, people, books, trees, dogs, chairs, walls, flowers, clouds, televisions. We see where each object is located, how large it is, and whether it is moving. We recognise familiar objects and also recognise when we see something we have never seen before. The visual system is able to perceive shapes, determine distances and detect movements; it tells us what something is, where it is located, and what it is doing.
Figure and ground Most of what we see can be classified as either object or background. Objects are things having particular shapes and particular locations in space. Backgrounds are in essence formless and serve mostly to help us judge the location of objects we see in front of them. Psychologists use the terms figure and ground to label an object and its background, respectively. The classification of an item as a figure or as a part of the background is not an intrinsic property of the item. Rather, it depends on the behaviour of the observer. If you are watching some birds fly overhead, they are figures and the blue sky and the clouds behind them are part of the background. If, instead, you are watching the clouds move, then the birds become background. If you are looking at a picture hanging on a wall, it is an object. Sometimes, we receive ambiguous clues about what is object and what is background. For example, do you think that Figure 6.1 illustrates two faces or a wine goblet? What are the characteristics of the complex patterns of light – varying in brightness, saturation and hue – that give rise to perceptions of figures, of things? One of the most important aspects of form perception is the existence of a boundary. If the visual field contains a sharp and distinct change in brightness, colour or texture, we
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Figure 6.3 Grouping. We tend to perceive a group of smaller elements as a larger figure.
Figure 6.1 A drawing in which figure and ground can be reversed. You can see either two faces against a white background or a goblet against a dark background.
In this figure, the orientation of the pie-shaped objects and the three 45-degree segments makes us perceive two triangles, one on top of the other. The one that looks like it is superimposed on the three black circles even appears to be brighter than the background. As you saw in Chapter 1, in the early twentieth century, a group of psychologists, Max Wertheimer (1880–1943), Wolfgang Kohler (1887–1967) and Kurt Koffka (1886–1941), devised a theory of perception called Gestalt psychology. Gestalt is
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perceive an edge. If this edge forms a continuous boundary, we will probably perceive the space enclosed by the boundary as a figure, as Figure 6.2 illustrates.
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Most figures are defined by a boundary. But the presence of a boundary is not necessary for the perception of form. Figure 6.3 shows that when small elements are arranged in groups, we tend to perceive them as larger figures. Figure 6.4 demonstrates illusory contours – lines that do not exist.
Figure 6.4 Illusory contours. Even when boundaries are not present, we can be fooled into seeing them. The triangle with its point down looks brighter than the surrounding area.
Figure 6.2 Form perception and boundaries. We immediately perceive even an unfamiliar figure when its outline is closed.
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the German word for ‘form’. They maintained that the task of perception was to recognise objects in the environment according to the organisation of their elements. They argued that in perception the whole is more than the sum of its parts. Because of the characteristics of the visual system of the brain, visual perception cannot be understood simply by analysing the scene into its elements. Instead, what we see depends on the relations of these elements to one another (Wertheimer, 1912). Elements of a visual scene can combine in various ways to produce different forms. Gestalt psychologists have observed that several principles of grouping can predict the combination of these elements. The fact that our visual system groups and combines elements is useful because we can then perceive forms even if they are fuzzy and incomplete. The real world presents us with objects partly obscured by other objects and with backgrounds that are the same colour as parts of the objects in front of them. The laws of grouping discovered by Gestalt psychologists describe the ability to distinguish a figure from its background. The adjacency/proximity principle states that elements that are closest together will be perceived as belonging together (Wertheimer, 1912). Figure 6.5 demonstrates this principle. The pattern on the left looks like five vertical columns because the dots are closer to their neighbours above and below them than to those located to the right and to the left. The pattern on the right looks like five horizontal rows. The similarity principle states that elements that look similar will be perceived as part of the same form. You can easily see the diamond inside the square in Figure 6.6. Good continuation is another Gestalt principle and refers to predictability or simplicity. For example, in Figure 6.7 it is simpler to perceive the line as following a smooth course than as suddenly making a sharp bend. Often, one object partially hides another, but an incomplete image is perceived. The law of closure states that our visual system often supplies missing information and ‘closes’ the outline of an incomplete figure. For example, Figure 6.8 looks a bit like a triangle, but if you
Figure 6.5 The Gestalt principle of proximity. Different spacing of the dots produces five vertical or five horizontal lines.
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Figure 6.6 The Gestalt principle of similarity. Similar elements are perceived as belonging to the same form.
place a pencil on the page so that it covers the gaps, the figure undeniably looks like a triangle. The final Gestalt principle of organisation relies on movement. The principle of common fate states that elements that move in the same direction will be perceived as belonging together and forming a figure. In the forest, an animal is camouflaged if its surface is covered with the same elements found in the background – spots of brown, tan and green – because its boundary is obscured. There is no basis for grouping the elements on the animal. As long as the animal is stationary, it remains well hidden. However, once it moves, the elements on its surface will move together, and the animal’s form will quickly be perceived.
Which path continues the line of black dots?
Figure 6.7 The Gestalt principle of good continuation. It is easier to perceive a smooth continuation than an abrupt shift.
Figure 6.8 The Gestalt principle of closure. We tend to supply missing information to close a figure and separate it from its background. Lay a pencil across the gaps and see how strong the perception of a complete triangle becomes.
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One explanation for our ability to recognise shapes of objects is that as we gain experience looking at things, we acquire templates, which are special kinds of visual memories stored by the visual system. A template is a type of pattern used to manufacture a series of objects (Selfridge and Neisser, 1960). When a particular pattern of visual stimulation is encountered, the visual system searches through its set of templates and compares each of them with the pattern provided by the stimulus. If it finds a match, it knows that the pattern is a familiar one. Connections between the appropriate template and memories in other parts of the brain could provide the name of the object and other information about it, such as its function, when it was seen before, and so forth.
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The template model of pattern recognition has the virtue of simplicity. However, it is unlikely that it could actually work because the visual system would have to store an unreasonably large number of templates. Despite the fact that you may look at your hand and watch your fingers wiggling about, you continue to recognise the pattern as belonging to your hand. How many different templates would your visual memory have to contain just to recognise a hand? Figure 6.9 illustrates this problem using the letter A. A more flexible model of pattern perception suggests that patterns of visual stimulation are compared with prototypes rather than templates. Prototypes (Greek for ‘original model’) are idealised patterns of a particular shape; they resemble templates but are used in a much more flexible way. The visual system does not look for exact matches between the pattern being perceived and the memories of shapes of objects but accepts a degree of disparity; for instance, it accepts the various patterns produced when we look at a particular object from different viewpoints.
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Figure 6.9 These four figures illustrate how template matching can fail. The position of the input may change (b), its size may change (c) or its orientation may change (d). Source: Neisser, U., Cognitive Psychology. New York: Appleton-Century-Crofts, 1967. Reprinted with permission.
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Most psychologists believe that pattern recognition by the visual system does involve prototypes, at least in some form. For example, you can probably identify maple trees, fir trees and palm trees when you see them. In nature, each tree looks different from all the others, but maples resemble other maples more than they resemble firs, and so on. A reasonable assumption is that your visual system has memories of the prototypical visual patterns that represent these objects. Recognising particular types of tree, then, is a matter of finding the best fit between stimulus and prototype. The visual system of the brain may indeed contain generic prototypes that help us recognise objects we have never seen before: coffee cups, maple trees, human faces. But we do more than recognise categories of objects; we can recognise particular coffee cups, maple trees or human faces. In fact, we can learn to recognise enormous numbers of objects. Think of how many different people you can recognise by sight, how many buildings in your town you can recognise, how many pieces of furniture in your house and in your friends’ houses you are familiar with – the list will be very long. Standing (1973) showed people 10,000 colour slides and found that they could recognise most of them weeks later, even though they had seen them just once.
Feature detection models Some psychologists suggest that the visual system encodes images of familiar patterns in terms of distinctive features – collections of important physical features that specify particular items (Selfridge, 1959). We are better at distinguishing some stimuli from others. We are better at searching for the letter A among a series of Bs than we are searching for the letter B among a series of As; we are better at finding orange-coloured objects in a series of red ones than vice versa; we find it easier to find a tilted item in a series of vertical items than finding a vertical item in a series of tilted ones. Similarly, we are better at finding a mobile object in a series of stationary ones than a stationary one in a series of mobile ones, we can detect bumps in a display of bumpy and flat surfaces better than we can the absence of bumps, and we are better at finding a single stimulus in an array of different stimuli when there are many more different stimuli. It appears, then, that some stimuli have more distinctive features than others and this enhances discrimination. Figure 6.10 contains several examples of the letter N. Although the examples vary in size and style, recognising them is not problematic because your visual system contains a specification of the distinctive features that fit the criterion for an N: two parallel vertical lines connected by
Figure 6.10 Distinctive features. We easily recognise all of these items as the letter N.
a diagonal line sloping downward from the top of the left one to the bottom of the right one. An experiment by Neisser (1964) supports the hypothesis that perception involves analysis of distinctive features. Figure 6.11 shows one of the tasks he asked people to do. The figure shows two columns of letters. The task is to scan through them until you find the letter Z, which occurs once in each column. You probably found the letter in the left column much faster than you did the one in the right column. Why? The letters in the left column share few features with those found in the letter Z, so the Z stands out from the others. In contrast, the letters in the right column have
GDOROC COQUCD DUCOQG GRUDQO OCDURQ DUCGRO ODUCQG CQOGRD DUZORQ UCGROD QCUDOG RQGUDO DRGOQC OQGDRU UGCODQ ODRUCQ UDQRGC ORGCUD
IVEMXW XVIWME VEMIXW WEKMVI XIMVWE IVMWEX VWEMXI IMEWXV EXMZWI IEMWVX EIVXWM WXEMIV MIWVXE IMEVXW IEMWVX IMWVEX XWMVEI IWEVXM
Figure 6.11 A letter-search task. Look for the letter Z hidden in each column. Source: Adapted from Neisser, J., Visual search. Scientific American Mind, 1964, 210, 94–102.
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many features in common with the target letter, and thus the Z is ‘camouflaged’. There are some phenomena that cannot easily be explained by the distinctive-features model. The model suggests that the perception of an object consists of analysis and synthesis; the visual system first identifies the component features of an object and then adds up the features to determine what the object is. We might expect, then, that more complex objects, having more distinctive features, would take longer to perceive. But often, the addition of more features, in the form of contextual cues, speeds up the process of perception. Figure 6.12 contains two sets of four items. One item in each is different from the other three. The patterns in both sets differ with respect to only one feature: the tilt of the diagonal line. But the addition of the horizontal and vertical lines in Figure 6.12 (b) makes the perceptual task much easier. We see a triangle and three right angles bisected by a diagonal line; the triangle just pops out as being different. If we perceived individual features (such as the diagonal lines) before perceiving more complex figures (such as triangles and bisected right angles) that are composed of these features, then we should perceive simpler figures faster than we perceive more complex ones. The fact that we do not means that a perception is not simply an assembly of individual features. The distinctive-features model appears to be a reasonable explanation for the perception of letters, but what about
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Figure 6.12 Contextual cues. Perceiving a simple stimulus is facilitated by contextual cues. The line that does not match the other three is more easily recognised in (b).
more natural stimuli, which we encounter in places other than the written page? Biederman (1987, 1990) suggests a model of pattern recognition that combines some aspects of prototypes and distinctive features. He suggests that the shapes of objects that we encounter can be constructed from a set of 36 different shapes that he refers to as geons. Figure 6.13 illustrates a few geons and some objects that can be constructed from them. Perhaps, Biederman suggests, the visual system recognises objects by identifying the particular sets and arrangements of geons that they contain. Even if Biederman is correct that our ability to perceive categories of common objects involves recognition of geons, it seems unlikely that the geons are involved in
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Figure 6.13 Geons for perception. (a) Several different geons. (b) The combination of two or three geons (indicated by the numbers) into common three-dimensional objects. Source: Adapted from Biederman, I., Higher-level vision. In An Invitation to Cognitive Science. Vol. 2: Visual Cognition and Action, edited by D.N. Osherson, S.M. Kosslyn and J. Hollerbach. Cambridge, MA: MIT Press, 1990.
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perception of particular objects. For example, it is difficult to imagine how we could perceive faces of different people as assemblies of different sets of geons. The geon hypothesis appears to work best for the recognition of prototypes of generic categories: telephones or torches in general rather than the telephone on your desk or the torch a friend lent you. Biederman points out that particular features of figures – cusps and joints formed by the ends of line segments – are of critical importance in recognising drawings of objects, presumably because the presence of these joints enables the viewer to recognise the constituent geons. Figure 6.14 shows two sets of degraded images of drawings of five common objects. One set, (a), shows the locations of cusps and joints; the other, (b), does not.
Biederman (1990) observed that people found the items with cusps and joints much easier to recognise.
Top-down processing: the role of context We often perceive objects under conditions that are less than optimum; the object is in a shadow, camouflaged against a similar background or obscured by fog. Nevertheless, we usually manage to recognise the item correctly. We are often helped in our endeavour by the context in which we see the object. For example, look at Figure 6.15. What do you see? Can you tell what they are? Now look at Figure 6.16. With the elements put in context it is quite easy to see what they are. Palmer (1975b) showed that even more general forms of context can aid in the perception of objects. He first showed his participants familiar scenes, such as a kitchen. Next, he used a tachistoscope to show them drawings of individual items and asked the participants to identify them. A tachistoscope can present visual stimuli very briefly so that they are difficult to perceive (nowadays we would use a computer to perform the same function). Sometimes, participants saw an object that was appropriate to the scene, such as a loaf of bread. At other times, they saw an inappropriate but similarly shaped object, such as a letterbox (see Figure 6.17).
Figure 6.15 Simple elements that are difficult to recognise without a context.
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Figure 6.14 Incomplete figures. (a) With cusps and joints. (b) Without cusps and joints. Which set is easier to recognise? Source: Adapted from Biederman, I., Higher-level vision. In An Invitation to Cognitive Science. Vol. 2: Visual Cognition and Action, edited by D.N. Osherson, S.M. Kosslyn and J. Hollerbach. Cambridge, MA: MIT Press, 1990.
Figure 6.16 An example of top-down processing. The context facilitates our recognition of the items shown in Figure 6.15. Source: Adapted from Palmer, S.E., in Explorations in Cognition, D.A. Norman, D.E. Rumelhart and the LNR Research Group. San Francisco: W.H. Freeman, 1975.
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Figure 6.17 Stimuli from the experiment by Palmer (1975b). After looking at the contextual scene, participants were shown one of the stimuli below it very briefly, by means of a tachistoscope. Source: Palmer, S.E., The effects of contextual scenes on the identification of objects. Memory and Cognition, 1975, 3, 519–26. Reprinted by permission of the Psychonomic Society, Inc.
Palmer found that when the objects fitted the context that had been set by the scene, participants correctly identified about 84 per cent of them. But when they did not, performance fell to about 50 per cent. Performance was intermediate in the no-context control condition, under which subjects did not first see a scene. Thus, compared with the no-context control condition, an appropriate context facilitated recognition and an inappropriate one interfered with it. The context effects demonstrated by experiments such as Palmer’s are not simply examples of guessing. That is, people do not think to themselves, ‘Let’s see, that shape could be either a letterbox or a loaf of bread. I saw a picture of a kitchen, so I suppose it’s a loaf of bread.’ The process is rapid, unconscious and automatic; thus, it belongs to the category of perception rather than to problem-solving, which is much slower and more deliberate. Somehow, seeing a kitchen scene sensitises the neural circuits responsible for the perception of loaves of bread and other items we have previously seen in that context. Psychologists distinguish between two categories of information-processing models of pattern recognition: bottom-up processing and top-down processing. In
bottom-up processing, also called data-driven processing, the perception is constructed out of the elements – the bits and pieces – of the stimulus, beginning with the image that falls on the retina. The information is processed by successive levels of the visual system until the highest levels (the ‘top’ of the system) are reached, and the object is perceived. Topdown processing refers to the use of contextual information – to the use of the ‘big picture’. Presumably, once the kitchen scene is perceived, information is sent from the ‘top’ of the system down through lower levels. This information excites neural circuits responsible for perceiving those objects normally found in kitchens and inhibits others. Then, when the subject sees a drawing of a loaf of bread, information starts coming up through the successive levels of the system and finds the appropriate circuits already warmed up, so to speak. Haenny et al. (1988) obtained direct evidence that watching for a particular stimulus can, indeed, ‘warm up’ neural circuits in the visual system. They trained monkeys to look at a pattern of lines oriented at a particular angle, to remember that pattern, and then to pick it out from a series of different patterns presented immediately afterwards. A correct response would be rewarded by a sip of fruit juice. While the animals were performing the task, the experimenters recorded the activity of individual neurons in the visual association cortex. They found that watching for a pattern of lines having a particular orientation affected the responsiveness of the neurons. For example, if the monkeys were watching for a pattern containing lines oriented at 45 degrees, neurons that detected lines of that orientation responded more vigorously than normal when that pattern was presented again. Haenny et al. found that this enhancement could even be produced by letting the monkeys feel the orientation of a pattern of grooves in a metal plate they could not see; when a subsequent visual pattern contained lines whose orientation matched that of the grooves, a larger neural response was seen. In most cases, perception consists of a combination of top-down and bottom-up processing. Figure 6.18 shows several examples of objects that can be recognised only by a combination of both forms of processing. Our knowledge of the configurations of letters in words provides us with the contexts that permit us to organise the flow of information from the bottom up.
Direct perception: Gibson’s affordances In the chapter so far we have considered some of the mechanisms that underlie visual perception. But is this perception a response or a process? That is, is visual perception an
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Although object perception is important to us, the perception of specific categories of yp sych stimuli may be even more important. One such category is ‘faces’. Being able to recognise and identify faces is one of the most important social functions human beings can perform (Bruce, 1994). It helps us form relationships with people, spot faces in a crowd and provides us with potential non-verbal cues as to what a person is thinking or feeling (the role of emotion in facial expression is returned to in Chapter 13). m
active or passive process? We saw in an earlier section on cross-cultural differences that context is important for visual perception. The psychologist J.J. Gibson took this notion a step further. Over a period of 35 years, Gibson proposed a theory of perception which argued that perception was direct and did not depend on cognitive processes to bring together fragmented data (Gibson, 1950, 1966, 1979). Because of this, it is considered a direct theory of perception. Originally, Gibson was interested in distinguishing between unsuccessful and successful Second World War pilots. Some of the unsuccessful pilots were unable to land accurately and seemed unable to appreciate distance. However, Gibson found that even when these pilots were given training in depth perception – which may have remedied the problem – they continued to have difficulty. According to Gibson, ‘perceiving is an act, not a response; an act of attention, not a triggered impression; an achievement, not a reflex’ (Gibson, 1979). Gibson’s view of perception was that classical optical
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Source: Adapted from McClelland, J.J., Rumelhart, D.E. and Hinton G.E., in Parallel Distributed Processing. Vol. 1: Foundations, edited by D.E. Rumelhart, J.L. McClelland and the PDP Research Group. © 1986 the Massachusetts Institute of Technology; published by the MIT Press, Cambridge, MA.
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Figure 6.18 Examples of combined top-down/bottom-up processing. The effect of context enables us to perceive the letters despite the missing or ambiguous features. Note that a given letter may be perceived in more than one way, depending on the letters surrounding it.
science ignored the complexity of real events. For example, it would focus on the effects of trivial, basic or simple stimuli on perceptual response. Gibson abandoned the depth/space perception view of the world and, instead, suggested that our perception of surfaces was more important. Surfaces comprised ground (which we discussed earlier) and texture elements in surfaces that would be attached or detached. Attached features would include bumps and indentations in the surface, such as rocks or trees; detached features would include items such as animals (which are detached from the surface). Given the complex world in which we live, we must be able to perceive not just simple stimuli but stimuli which mean something more to us. We must decide whether an object is throwable or graspable, whether a surface can be sat upon and so on. We ask ourselves what can this object furnish us with, what does it afford us (Gibson, 1982)? These are the meanings that the environment has and Gibson called them affordances. Thus, Gibson highlighted the ecological nature of perception: we do not simply perceive simple stimuli but these stimuli mean something more in a wider, more complex context. This was a radical departure in visual perception because it implied that the perception of object meaning is direct. Perception involves determining whether something is capable of being sat upon or is throwable. However, the theory is not without its problems. Costall (1995), for example, suggests that some affordances may not be able to afford. Imagine the ground covered in frost and a frozen lake. According to Gibson, the ground afforded walking. However, although the frosty ground does, the frozen lake may not. Similarly, although we might agree with Gibson that some surfaces are graspable or supporting we might disagree quite reasonably with the notion that surfaces are edible, for example, that they afford eating. Our decision that something is edible appears to rely on more than direct perception of surfaces.
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Thompson created his stimuli using the face of the British Prime Minister). Women and girls tend to be better than men and boys at decoding people’s facial expression of emotion (McClure, 2000). Women are better at identifying upright faces even when they are masked by visual noise or when there is a delay between the presentation of the face and recall (McBain et al; 2009). Figure 6.20 illustrates some of the stimuli in McBain et al’s experiment.
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Psychologists in the nineteenth century were interested in what makes a face attractive and constructed composites – averages of several different images – to produce a face which they believed was attractive (Galton, 1878; Stoddard, 1886). Recent work has provided a clearer account of what makes an attractive face; it has also helped to indicate which features of the face best allow us to remember a face or which make a face distinctive. We can identify people better on the basis of the eyes than the mouth and both are more important than the nose (Bruce et al., 1993), even when hairstyle, make-up and facial hair are removed or minimised. A threedimensional image of a face – such as that seen in three-quarter profile – is better recognised than is a fullfrontal photograph. Upright faces are better recognised and identified than are those upside down but there is a curious phenomenon called the ‘Thatcher effect’, first described by the British psychologist, Peter Thompson (1980). Take a look at the faces in Figure 6.19. They look fairly normal – you can easily identify the image as a face and, while you can see that the faces are inverted, the features appear to be in the right place, and are identifiable. Now, turn the book upside down and look at the photographs again. It is a grotesque image, but only eyes and the mouth have been turned around (inverted) to create this effect. This is the Thatcher effect (so-called because
We can usually discriminate between faces more quickly on the basis of their users’ sex than familiarity (Bruce et al., 1987). Enlow (1982) and Moss et al. (1987), for example, have suggested that men have larger noses and nasopharynxes, more prominent brows, a more sloping forehead and more deeply set eyes than do women. Shepherd (1989) noted that women had fuller cheeks and less facial hair (including eyebrows). Women are also thought to have smaller noses, a more depressed bridge of the nose, a shorter upper lip, and larger eyes with darker shadows, especially young women (Liggett, 1974). When facial features are presented in isolation, eyes are the most reliable indicator of sex and the nose is the least reliable. With hair concealed, 96 per cent of partici-
Figure 6.19 The Thatcher effect – turn the page upside down to experience the effect. Source: Grüter, T., Grüter, M. and Carbon, C-C. Neural and genetic foundations of face recognition and prosopagnosia. Journal of Neuropsychology (2008), 2, 79–97, figure 3.
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Figure 6.20 (a) Face images utilised in the standard and delayed conditions of the facial identity discrimination task. (b) Face images utilised in the visual noise condition of the facial identity discrimination task. Source: McBain, R, Norton, D. and Chen, Y. Females excel at basic face perception. Acta Psychologica (2009), 130, 168–73, figure 3.
pants were able to distinguish between faces based on sex (Burton et al., 1993). When individual facial features or pairs of features (such as brow and eyes, nose and mouth) were presented to participants, the features which afforded the best opportunity to make sex discriminations were, in this order: brow and eyes, brow alone, eyes alone, whole jaw, chin, nose and mouth, and mouth alone (Brown and Perrett, 1993). These findings suggest that all facial features carry some information about sex (except the nose) but suggest that it is difficult to find even one or two features which distinguish absolutely between men’s and women’s faces. Some features, however, provide better clues than others.
Distinctiveness and attractiveness Each of us finds different faces attractive: some of us find faces friendlier than others, some meaner and others more sexually alluring. Although individual differences exist at this, what seems like, subjective level, studies have shown that some features of the face are generally regarded as more attractive than others. The distinctiveness of the face – defined as the deviation from the norm – is unrelated to attractiveness (Bruce et al., 1994). Galton had hypothesised that averageness was attractiveness. That is, the more average-looking the face, the more attractive it was likely to be. This hypothesis was tested and challenged by Perrett et al. (1994), who compared the attractiveness ratings for average, attractive and highly attractive Caucasian female faces.
Perrett et al., using special computer technology, constructed an average composite of photographs of 60 female faces. The 15 faces rated as most attractive from the original 60 were then averaged. Finally, the attractiveness of this average was enhanced by 50 per cent to provide a ‘highly attractive’ composite. Composites similar to those used in the experiment can be seen in Figure 6.21. Caucasian raters found the ‘attractive’ composite more attractive than the average composite and the highly attractive composite more attractive than the ‘attractive’ composite, thus disconfirming Galton’s hypothesis. Furthermore, when similar composites were made of Japanese women, the same results were obtained: both Caucasian and Japanese raters found the enhanced composite more attractive. What distinguished an average face from an attractive one? Analysis of the composites showed that the more attractive faces had higher cheek bones, a thinner jaw and larger eyes relative to the size of the face. There was also a shorter distance between mouth and chin and between nose and mouth in the attractive faces. Evolutionary psychologists argue that we are attracted to average faces because this behaviour evolved as a solution to attracting healthy mates – best to stick with what you know and can trust. An alternative view is that we are simply attracted to the familiar – a well-known psychological phenomenon. If this were true, we should be attracted to average-looking stimuli that are non-faces too. This is what Halberstadt and Rhodes (2000) found. They asked people to rate a selection of watches, birds and dogs for attractiveness and
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Figure 6.21 Faces similar to those used in Perrett et al.’s (1994) experiment. The faces are ‘morphed’ from averagely attractive (top two faces) to very attractive (bottom two faces). Most people rate the last two faces as most attractive. Source: From Young, A.W. and Bruce, V., Pictures at an exhibition: The science of the face. The Psychologist, 1998, 11(3), 120–5 (see www.thepsychologist.org.uk).
prototypicality (how typical they were of a category), or averageness. The researchers found that participants rated the average-looking stimuli as being the most attractive. One reason for this may be that we have a preference for averageness which ‘reflects a more general preference for familiar stimuli’. In one experiment, Caucasian participants rated their own-race face-composites as more attractive than those of other races but this finding was limited to the male faces (Rhodes et al., 2005). When average composites of Caucasian and Japanese faces were judged, Caucasians preferred the mixed race composite, especially if the face was of the opposite sex. Japanese and Caucasian participants, asked to judge the attractiveness of Caucasian and Japanese faces (from extremely Caucasian and Japanese, to the other end of the continuum) rated the mixed-race composite as most attractive. Does the attractiveness of a face actually have consequences for us, beyond immediate physical liking for a person? Langlois et al. (2000) analysed over 900 studies of people’s behaviour towards attractive and unattractive individuals. They found that not only was there agreement between people and cultures about who is attractive and who is not, but also that attractive children and adults were treated and judged more positively than were unattractive children and adults (even when people knew the unattractive individuals). Although turning hoary maxims such as ‘beauty is in the eye of the beholder’ on its head, Langlois et al. note that the studies they reviewed categorised people into either attractive or unattractive only. Gradations of attractiveness may have elicited different responses in people so that averagely attractive people may have elicited more positive responses than their excessively attractive or unattractive counterparts. There is also mixed evidence regarding the type of ‘sexual’ face that we like: some studies suggest that we prefer more feminised faces; others that we like masculinised ones (Johnston, 2006). The explanation for our preference for feminised faces is that they are more youthful, warm and honest; masculinised faces are more cold, dominant, dishonest. Faces morphed to look younger are rated as significantly more attractive (Ishi et al., 2004). Attractive faces whose gaze is direct can have a knockon positive effect on our judgements of unrelated objects (Strick et al., 2008). A directly gazing face is considered significantly more attractive than an indirectly gazing one. We also like objects more if we see a person smiling at them than if they show disgust. Furthermore, we are more likely to engage socially with people if they look at us directly. Strick et al. paired novel objects – pictures of unknown peppermint brands – with an attractive or unat-
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tractive face which looked straight at the participant or which averted its gaze. Participants rated the attractiveness of these objects. As predicted, objects paired with a directly gazing attractive face were more positively evaluated than were objects paired with an indirectly gazing attractive face or an unattractive face. We also, naturally, spend more time looking at beautiful faces than unattractive ones, but a study from a group of US researchers has found that although women spend more time looking at beautiful male and female faces than they do unattractive ones, men spend longer than women looking at beautiful female faces (Levy et al., 2008). What do you find attractive in an attractive face? Do your preferences match those found in experimental studies? Do you think that some facial features we find attractive are so subtle that we cannot consiously detect them?
Face preference and menstrual cycle When we see faces, we normally make judgements about them – some studies show that women prefer exaggeratedly masculine male faces whereas some studies show that men and women prefer ‘average-looking’ faces. Women’s preference for men’s faces can change across the menstrual cycle. Penton-Voak and Perrett (2000) found that women in the follicular phase of their cycle were significantly more likely to prefer a masculine face than those in menses or in the luteal phase. This, the authors provocatively suggest, shows that ‘women are attracted to relatively exaggerated male traits when conception following coitus is more likely (days 6–14 of the follicular phase) and not at other times in the menstrual cycle’. One explanation for the preference is that during this fertile phase of the cycle, women are more likely to seek a sexual partner (and, potentially, a father for their child) who shows evidence of ‘genetic benefits’ (strength, assertiveness, etc.). This explanation is based on limited experimental data, however, and more direct behaviour – such as the interaction between men and women – has not been studied. Gangestad et al. (2004) found that women during the high fertility portion of their menstrual cycle were more attracted to men who showed social presence and ‘intrasexual competitiveness’ than in their low fertility days. Social presence was characterised by composure, having an athletic presence, maintaining eye contact, lack of selfdeprecation, lack of downward gaze and ‘lack of nice-guy self-presentation’. Direct intrasexual competitiveness was defined by behaviours that derogated competitors, lacked laughter and were directly sexually competitive. This pref-
erence only emerged when women wished short-term rather than long-term relationships, suggesting that a man’s demeanour can significantly alter perceived attractiveness by women high in fertility, but this attraction may be short-lived. A study of 70 young women has found that their level of a hormone called testosterone (described in Chapter 13) is related to how attractive they found others: the greater the testosterone, the greater their attraction to masculine faces (Welling et al., 2007). Another study has found that although very masculine male faces are judged to be dominant, their owners are less likely to be judged suitable as a long-term partner by women than are owners of less masculine faces (Boothroyd et al., 2007). The group also measured women’s judgements of the attractiveness of men’s faces across various points of their menstrual cycle. Symmetrical faces are usually judged to be more attractive than asymmetrical ones and there is evidence that facial symmetry in men and women is associated with perceived healthiness (Rhodes et al., 2007) and self-reported extraversion (Pound et al., 2007). The researchers found that women preferred more symmetrical faces when the women were at their most fertile but this preference was found only when the women were seeking a short-term partner or if the women already had a partner (Little et al., 2007). The results suggest that this facial feature may maximise mating by encouraging short-term relationships.
Theories of face perception The mechanisms that allow us to perceive faces are considered to be different from those that allow us to perceive objects; face perception has been thought of as ‘special’ (Farah et al., 1998). Face perception involves a number of operations. We can perceive general characteristics such as the colour, sex and age of a face; we can perceive whether a face expresses anger, sadness or joy; we can distinguish familiar from unfamiliar faces. What model of face processing can account for these operations? Bruce and Young (1986) have suggested that face processing is made up of three functions: perception of facial expression, perception of familiar faces and perception of unfamiliar faces. Why does the model separate these functions? Bruce and Young reviewed extensive evidence which suggested that each of these functions is dependent on different cognitive abilities. Evidence from neuropsychology also supports such a model. Some patients with right hemisphere damage, as we will see later in the chapter, can perceive and correctly identify emotion in facial expressions, and the sex and age
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Figure 6.22 The principal monocular and binocular depth cues. Source: From Margaret W. Matlin and Hugh H.J. Foley, Sensation and Perception, 3rd edn © 1992. Published by Allyn & Bacon, Boston, MA. Copyright © by Pearson Education. By permission of the publisher.
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Depth perception requires that we perceive the yp sych distance of objects in the environment from us and from each other. We do so by means of two kinds of cues: binocular (‘two-eye’) and monocular (‘one-eye’). Binocular cues arise from the fact that the visual fields of both eyes overlap. Only animals that have eyes on the front of the head (such as primates, cats and some birds) can obtain binocular cues. Animals that have eyes on the sides of their heads (such as rabbits and fish) can obtain only monocular cues. One monocular cue involves movement and thus must be experienced in the natural environment or in a motion picture. The other monocular cues can be represented in a drawing or a photograph. Most of these cues were originally discovered by artists and only later studied by psychologists (Zeki, 1998). Figure 6.22 shows the most important sources of depth cues.
Binocular cues In addition to being able to perceive the forms of objects in our environment, we are able to judge quite accurately their relative location in space and their movements. Perceiving where things are and perceiving what they are
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doing are obviously important functions of the visual system (Decety et al., 1997; Jeannerod, 1997).
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of faces, but they cannot identify faces (Tranel et al., 1988). In a classic study, Young et al. (1993) studied face perception in ex-servicemen who had sustained missile wounds to the posterior left and right hemispheres. They administered a series of face perception tests which included tests of familiar face identification, matching unfamiliar faces and facial expression identification. The experimenters found that one patient was poor at identifying familiar faces only, another was selectively poor at matching unfamiliar faces and a group of men was impaired at analysing facial expressions. Current views of face processing argue that we exploit three strategies when we recognise faces. One strategy involves recognising the features of a face, a second involves recognising the relations between features in a face (configural processing) and a third suggests that we recognise the whole face (the holistic approach) (Gruter et al., 2008). Configural processing works when faces are upright, but fails when they are inverted, à la the Thatcher effect.
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visual scene. If an object is very close to your face, your eyes are turned inwards. If it is farther away, they look more nearly straight ahead. Thus, the eyes can be used like range finders. The brain controls the extraocular muscles, so it knows the angle between them, which is related to the distance between the object and the eyes. Convergence is most important for perceiving the distance of objects located close to us, especially those we can reach with our hands (see Figure 6.23). Another important factor in the perception of distance is the information provided by retinal disparity (‘unlikeness’ or ‘dissimilarity’). Hold up a finger of one hand at arm’s length and then hold up a finger of the other hand midway between your nose and the distant finger. If you look at one of the fingers, you will see a double image of the other one. Whenever your eyes are pointed towards a particular point, the images of objects at different dis-
tances will fall on different portions of the retina in each eye. The amount of disparity produced by the images of an object on the two retinas provides an important clue about its distance from us. The perception of depth resulting from retinal disparity is called stereopsis. A stereoscope is a device that shows two slightly different pictures, one for each eye. The pictures are taken by a camera equipped with two lenses, located a few inches apart, just as our eyes are. When you look through a stereoscope, you see a three-dimensional image. An experiment by Julesz (1965) demonstrated that retinal disparity is what produces the effect of depth. Using a computer, he produced two displays of randomly positioned dots in which the location of some dots differed slightly. If some of the dots in one of the displays were displaced slightly to the right or the left, the two displays gave the impression of depth when viewed through a stereoscope.
B Angle A is larger than angle B; therefore the apple is perceived as closer A
Figure 6.23 Convergence. When the eyes converge on a nearby object, the angle between them is greater than when they converge on a distant object. The brain uses this information in perceiving the distance of an object.
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Figure 6.24 shows a pair of these random-dot stereograms. If you look at them very carefully, you will see that some of the dots near the centre have been moved slightly to the left. Some people can look at these figures without using a stereoscope and see depth. If you want to try this, hold the book at arm’s length and look at the space between the figures. Now pretend you are looking ‘through’ the book, into the distance. Each image will become double, since your eyes are no longer converged properly. If you keep looking, you might make two of these images fuse into one, located right in the middle. Eventually, you might see a small square in the centre of the image, raised above the background.
Monocular cues One of the most important sources of information about the relative distance of objects is interposition (meaning ‘placed between’). If one object is placed between us and another object so that the closer object partially obscures our view of the more distant one, we can immediately perceive which object is closer to us. Obviously, interposition works best when we are familiar with the objects and know what their shapes should look like. Just as the Gestalt law of good continuation plays a role in form perception, the principle of good form affects our perception of the relative location of objects: we perceive the object having the simpler border as being closer. Figure 6.25 (a) can be seen either as two rectangles, located one in front of the other (Figure 6.25 (b)), or as a rectangle nestled against an L-shaped object (Figure 6.25 (c)). Because we tend to perceive an ambiguous drawing according to the principle of good form, we are more likely to perceive Figure 6.25 (a) as two simple shapes – rectangles – one partly hiding the other.
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Figure 6.24 A pair of random-dot stereograms. Source: Julesz, B., Texture and visual perception. Scientific American, 212, 1965, 12, 38–48. © 1965 Scientific American, Inc. Reprinted with permission of Dr. Bela Julesz.
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Figure 6.25 Use of the principle of good form in the perception of depth. The two objects shown in (a) could be two identical rectangles, one in front of the other, as shown in (b) or a rectangle and an L-shaped object, as shown in (c). The principle of good form states that we will see the ambiguous object in its simplest (best) form – in this case a rectangle. As a result, the shape to the right is perceived as being partly hidden and thus further away from us.
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Another important monocular distance cue is provided by our familiarity with the sizes of objects. For example, if a car casts a very small image on our retinas, we will perceive it as being far away. Knowing how large cars are, our visual system can automatically compute the approximate distance from the size of the retinal image. Figure 6.26 shows two columns located at different distances. The drawing shows linear perspective: the tendency for parallel lines that recede from us to appear to converge at a single point. Because of perspective, we perceive the columns as being the same size even though they
Figure 6.26 Principle of perspective. Perspective gives the appearance of distance and makes the two columns look similar in size.
produce retinal images of different sizes. We also perceive the segments of the wall between the columns as rectangular, even though the image they cast on the retina does not contain any right angles. Texture, especially the texture of the ground, provides another cue we use to perceive the distance of objects sitting on the ground. A coarser texture looks closer, and a finer texture looks more distant. The earth’s atmosphere, which always contains a certain amount of haze, can also supply cues about the relative distance of objects or parts of the landscape. Parts of the landscape that are further away become less distinct because of haze in the air. Thus, haze provides a monocular distance cue (see Figure 6.27). The patterns of light and shadow in a scene – its shading – can provide us with cues about the three-dimensional shapes of objects. Although the cues that shading provides do not usually tell us much about the absolute distances of objects from us, they can tell us which parts of objects are closer and which are further away. Figure 6.28 illustrates the power of this phenomenon. Some of the circles look as
Figure 6.27 Cues from atmospheric haze. Variation in detail, owing to haze, produces an appearance of distance. Source: Powerstock SuperStock, reprinted by permission.
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if they bulge out towards us; others look as if they were hollowed out (dimpled). The only difference is the direction of the shading. Our visual system appears to interpret such stimuli as if they were illuminated from above. Thus, the top of a convex (bulging) object will be light and the bottom will be in shadow. If you turn the book upsidedown, the bulges and dimples will reverse. These features are important to practical aspects of our lives, an example of which appears in the Psychology in Action section below.
Figure 6.28 Depth cues supplied by shading. If the tops of the circles are dark, they look like depressions. If the bottoms are dark, they appear as bumps.
Psychology in action – CCTV and face perception facial areas such as the eye sockets and nostrils. In fact, lighting of this sort makes the face look like a negative. This study highlights an important point about face perception (and about the erroneous testimony described at the opening of the chapter). Our recognition of faces is not simply based on ‘edge’ information, that is, on contour. The shape of the face (viewpoint) and shading are crucial in enabling us to make accurate recognition judgements. Is recognition improved if the face is moving? After all, a moving image might give more information about shading, shape and contour than would a static one. Some researchers have reported that a moving image is more advantageous to accurate recognition than is a static one (Pike et al., 1997; Knight and Johnston, 1997). Others have found little improvement in recognition when moving and static images are compared (Christie and Bruce, 1998). Recognition is also enhanced by familiarity. Burton et al. (1999) took video footage of male and female university psychology lecturers caught on security cameras at the entrance to the psychology department. They then asked psychology and non-psychology students, as well as experienced police officers, to view this footage and then asked them to indicate which of the people in a set of high-quality photographs they had seen on tape. Psychology students made more correct identifications than did the non-psychology students or police officers, suggesting that previous familiarity with the target helps with recognition. In the second experiment, the researchers looked at which specific bits of information the participants used to identify the target. They took the same video footage, but this time they either obscured the head, the body or the gait.
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Imagine that you are spending your Saturday afternoon in a busy shopping centre. Browsing in a store, you spot a particularly attractive shirt and take it to the sales counter. When you place the shirt and your wallet/purse on the counter, you feel someone nudge you from behind. You turn around but when you return to the shirt on the counter, you notice that your wallet/purse has disappeared. A person whose face you partly see is running out of the store. Fortunately, the police manage to apprehend a suspect and the store detective informs you that he has video surveillance footage of a man who might be the thief. The suspect does not have your wallet but the image on the surveillance camera looks like the suspect. How accurately would you be able to match the suspect to the image on the video screen? The increasing use of CCTV has led to an increase in the reliance on CCTV evidence in prosecutions but CCTV footage is usually variable in quality with camera angles and lighting conditions producing an unclear image of the top or back of the head (Bruce, 1998). Changing the lighting conditions reduced performance in a task which required individuals to match the face they had seen with a photograph (Hill and Bruce, 1996). Changing the viewpoint also impaired recognition accuracy but changing both lighting and viewpoint did not make performance any worse. According to a 2009 UK Home Office and police report, around 80 per cent of CCTV images are of no practical use because they are of such poor quality. Matching faces (and even recognising familiar surfaces) was more accurate when lighting was from above. Why? One explanation is that light from above provides more information by casting fewer shadows. Hill and Bruce (1996) suggest that lighting a face from the bottom reverses the brightness of
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Psychology in action – Continued Participants performed quite inaccurately when gait and body were obscured but were significantly worse at identifying the target when the head was obscured. Thus the advantage of familiarity – at least, in this experiment – was due to recognition of facial features rather than the way in which people walk or their body shape. Unusual gaits or shapes may produce different results. When people watched CCTV footage of a person and then tried to match the image in the footage with either a single snapshot or an array of snapshots, people performed the task poorly (Bruce et al., 2001). However, when the participants knew the person in the footage – the targets were the participants’ teachers or colleagues – they were significantly better at the task. Even in experiments where participants were made briefly familiar with the image they were exposed to, this period of familiarisation did not help the participant recognise the face. According to Bruce et al. (2001), ‘where a person is recognised on a CCTV image by someone familiar to them, these identifications should be taken very seriously, even if the CCTV image is of low quality’. They refer to the case of the London nail bomber, David Copeland, as an illustration of this finding. Copeland was responsible for killing three people and injuring 129 others in nail bomb explosions in three areas of London – Soho, Brick Lane and Brixton – in the spring of 1999. Copeland’s final crime was committed in the Admiral Duncan pub in Soho, Central London. He left the pub at 6.05 p.m. The bomb exploded as Copeland made his way back to his hotel. Three people were killed, four required amputations and 26 suffered burns (Hopkins and Hall, 2000). Eighty minutes before the bomb was detonated Copeland’s colleague had telephoned the police and told them that he thought the bomber identified on CCTV and publicised on television looked like his workmate. By that evening, police were planning a raid on Copeland’s house.
Bruce et al.’s research suggests that this use of CCTV may be one of its most effective.
The site of the bomb placed by David Copeland. Copeland was apprehended after a colleague recognised his face from CCTV footage shown on television. Research suggests that recognition of people seen in CCTV footage is significantly more accurate if these people are familiar. If the target person is not familiar, the likelihood of false positives (making an incorrect identification) increases. Source: Metropolitan Police Service
Distance and location When we are able to see the horizon, we perceive objects near it as being distant and those above or below it as being nearer to us. Thus, elevation provides an important monocular depth cue. For example, cloud B and triangle B in Figure 6.29 appear further away from us than do cloud A and triangle A. So far, all the monocular distance cues discussed have been those that can be rendered in a drawing or captured by a camera. However, another important source of distance information depends on our own movement. Try
the following demonstrations. If you focus your eyes on an object close to you and move your head from side to side, your image of the scene moves back and forth behind the nearer object. If you focus your eyes on the background while moving your head from side to side, the image of the nearer object passes back and forth across the background. Head and body movements cause the images from the scene before us to change; the closer the object, the more it changes relative to the background. The information contained in this relative movement helps us to perceive distance.
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Figure 6.29 Depth cues supplied by elevation. The objects nearest the horizontal line appear furthest away from us. Source: Adapted from Matlin, M.W. and Foley, H.J., Sensation and Perception (3rd edn). Boston: Allyn & Bacon, 1992.
Figure 6.30 illustrates the kinds of cue supplied when we move with respect to features in the environment. The top part of the figure shows three objects at different distances from the observer: a man, a house and a tree. The lower part shows the views that the observer will see from five different places (P1–P5). The changes in the relative locations of the objects provide cues concerning their distance from the observer. The phenomenon is known as motion parallax (parallax comes from a Greek word meaning ‘change’).
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Visual perception across cultures From birth onwards, we explore our environment with our eyes. The patterns of light and dark, colour and movement, produce changes in the visual system of the brain. There is evidence, however, that perception is not absolute, that it varies across cultures. Ecological variables such as those associated with geography, cultural codes and education influence perception.
The visual stimulation we receive, particularly during infancy, affects the development of our visual system. If the environment lacks certain features – certain visual patterns – then an organism might fail to recognise the significance of these features if it encounters them later in life (Blakemore and Mitchell, 1973). But this is not the only type of environment that can influence perception. There may also be differences in the cultural codes found in pictorial representations (Russell et al., 1997). Although artists have learned to represent all the monocular depth cues (except for those produced by movement) in their paintings, not all cues are represented in the traditional art of all cultures. For example, many cultures do not use linear perspective. Does the absence of particular cues in the art of a particular culture mean that people from this culture will not recognise them when they see them in paintings from another culture? It is quite rare for a member of one culture to be totally unable to recognise a depiction as a depiction (Russell et al., 1997). However, Deregowski et al. (1972) found that when the Me’en tribe of Ethiopia, a culture unfamiliar with pictures, were shown a series of pictures from a children’s colouring book, they would smell them, listen to the pages while flexing them, examine their texture but would ignore the actual pictures. They did recognise depictions of indigenous animals, suggesting that the familiarity of a pictorial depiction is important for recognition within cultures. Familiar objects are sometimes depicted in an exaggerated way. Aboriginal depictions of the crocodile, for example, are distorted: the trunk is seen from above and the head and tail from the side (Dziurawiec and Deregowski, 1992), although this finding may be attributable to the fact that such animals are difficult to draw. There are other geographical influences on perception. People who live in ‘carpentered worlds’, that is worlds in which buildings are built from long, straight pieces of material that normally join each other in right angles, are more likely to be subject to the Müller–Lyer illusion. This illusion is shown in Figure 6.31. Look at the two vertical lines and decide which is longer. Actually, the lines are of equal length. Segall et al. (1966) presented the Müller–Lyer illusion (and several others) to groups of subjects from Western and nonWestern cultures. Most investigators believe that the Müller–Lyer illusion is a result of our experience with the angles formed by the intersection of walls, ceilings and floors (Redding and Hawley, 1993). The angled lines can be seen as examples of linear perspective (see Figure 6.32). In fact, Segall and his colleagues did find that people from ‘carpentered’ cultures were more susceptible to this illusion: experience with straight lines forming right angles appeared to affect people’s perception.
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Viewpoints P1
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Figure 6.30 Motion parallax. As we move from P1 to P5, the relative locations of the man, tree and house change. These changes enable us to make inferences about the relative positions of these objects. Source: From HABER, Psychology of Visual Perception, 1st ed. (c) 1973 Wadsworth, a part of Cengage Learning, Inc. reproduced by permission, www.cengage.com/permissions
Figure 6.31 The Müller–Lyer illusion. The two vertical lines are actually equal in length, but the one on the left appears to be longer.
Figure 6.32 The impact of culture on the Müller–Lyer illusion. People from ‘non-carpentered’ cultures that lack rectangular corners are less likely to be susceptible to this illusion. Although the two vertical lines are actually the same height, the one on the right looks shorter.
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Controversies in Psychological Science – How does language influence visual perception? The effects on perception of another cultural code – language – have received much attention from psychologists for a good reason. Words for shades of light and colour seem to be more limited in some cultures than others. The Inuit, for example, have more than one name for various shades of snow, whereas Africans have different words for different shades of sand, presumably because these features form a crucial part of the culture’s environment. There are also differences in the number of colour words that different cultures use. This has important implications for our understanding of the crosscultural generalisability of colour perception which we discussed in Chapter 5. For example, do all cultures use all the primary and secondary colour terms? Does the word ‘blue’ mean the same across cultures? Do cultures have different words for various shades of blue? If so, why?
The evidence In the mid-nineteenth century, the British statesman William Gladstone noted that the writings of the ancient Greeks did not contain words for brown or blue. Perhaps the ancient Greeks did not perceive these colours. Magnus (1880) investigated this hypothesis by gathering both linguistic and perceptual data. He sent questionnaires and colour chips to Western residents of European colonies and asked them to test the abilities of the native people to distinguish among the various colours. He assumed that language would reflect perceptual ability. If a language did not contain words to distinguish between certain colours, then the people who belonged to that culture would not be able to distinguish these colours perceptually. Magnus was surprised to discover very few cultural differences in people’s ability to perceive various colours. Linguistic differences did not appear to reflect perceptual differences. The issue emerged again in the mid-twentieth century with the principle of linguistic relativity. Briefly stated, this principle asserts that language used by the members of a particular culture is related to these people’s thoughts and perceptions. The bestknown proponent of this principle, Benjamin Whorf, stated that ‘the background linguistic system. . . of each language is not merely a reproducing instrument for voicing ideas but rather is itself a shaper of ideas, the program and guide for the individual’s mental activity, for his analysis of impressions, for his synthesis of his mental stock-of-trade’ (Whorf, 1956, p. 212). This became known as the Sapir–Whorf hypothesis – the idea that language can determine thought (Kay and Kempton, 1984). Proponents of linguistic relativity suggested that colour names were cultural conventions – that members of a given culture could divide the countless combinations of hue, satura-
tion and brightness (defined in Chapter 5) that we call colours into any number of different categories (Kay et al., 1997). Each category was assigned a name, and when members of that culture looked out at the world, they perceived each of the colours they saw as belonging to one of these categories. Two anthropologists, Berlin and Kay, examined this hypothesis in a linguistic study of a wide range of languages. They found the following eleven primary colour terms: black, white, red, yellow, green, blue, brown, purple, pink, orange and grey (Berlin and Kay, 1969; Kay, 1975; Kay et al., 1991). The authors referred to these as focal colours. Not all languages used all eleven (as English does). In fact, some languages used only two: black and white (Heider, 1972). Others, such as Russian, had two words for blue. If a language contained words for three primary colours, these colours were black, white and red. If it contained words for six primary colours, these were black, white, red, yellow, green and blue. Berlin and Kay suggested that basic colour terms would be named more quickly than non-basic colour terms, that basic terms would be more salient, that is, they would be elicited first if you asked people to name colours spontaneously, and that basic terms would be more common in written communications such as texts. In fact, people do respond more quickly to basic than they do to non-basic colour terms across a range of languages; when asked to write down a list of as many colour words in five minutes as possible and draw a line under the last words written, every minute, basic terms invariably appear at the beginning of the list (Corbett and Davies, 1997). Similarly, Heider (1971) found that both children and adults found it easier to remember a colour chip of a focal colour (such as red or blue) than one of a non-focal colour (such as turquoise or peach). In a famous cross-cultural study, Heider (1972) studied members of the Dani culture of New Guinea. The language of the Dani people has only two basic colour terms: mili (‘black’) and mola (‘white’). Heider assembled two sets of colour chips, one containing focal colours and the other containing nonfocal colours. She taught her participants arbitrary names that she made up for the colours. Even though the participants had no words in their language for any of the colours, the group learning names for focal colours learned the names faster and remembered them better. Categorical perception of colour refers to our ability to discriminate between two colours that seem to fall along a continuum. However, speakers of Berinmo and Himba do not distinguish a boundary between green and blue, which suggests that categorical perception is not universal. Roberson et al. (2008) tested this hypothesis in a group of native Koreanand English-speaking adults. Koreans distinguish between
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Controversies in Psychological Science – Continued yeondu and chorok. The boundary between the two was described as ‘green’ by English speakers. Korean speakers were faster at discriminating between colours marked as a boundary in Korean but not English, but not at distinguishing between colours that fell within a colour category. The faster participants showed categorical perception only when stimuli appeared in the right visual field; slower participants showed categorical perception in both visual fields, suggesting that categorical perception may be verbally mediated by the left hemisphere.
Brightness constancy People can judge the whiteness or greyness of an object very well, even if the level of illumination changes. If you look at a sheet of white paper either in bright sunlight or in shade, you will perceive it as being white, although the intensity of its image on your retina will vary. If you look at a sheet of grey paper in sunlight, it may in fact reflect more light to your eye than will a white paper located in the shade, but you will still see the white paper as white and the grey paper as grey. This phenomenon is known as brightness constancy. Katz (1935) demonstrated brightness constancy by constructing a vertical barrier and positioning a light source so that a shadow was cast to the right of the barrier. In the shadow, he placed a grey square card on a white background. In the lighted area on the left of the barrier, he placed a number of shades of grey and asked participants to choose one that matched the grey square in the shadow (see Figure 6.33).
Figure 6.33 Brightness constancy as demonstrated by the experiment by Katz (1935).
Conclusion Colour is a difficult topic to study cross-culturally. The evidence suggests, however, that although there are cultural variations in the number of colour words used, there seems to be crosscultural agreement on the colours considered as ‘basic’.
His participants matched the greys not in terms of the light that the cards actually reflected but in terms of the light they would have reflected had both been viewed under the same level of illumination. In other words, the participants compensated for the dimness of the shadow. The match was not perfect, but it was much closer than it would have been if perception of brightness had been made solely on the basis of the amount of light that fell on the retina. The perception of white and grey, then, is not a matter of absolutes; rather, the colours are perceived relative to the surrounding environment.
Form constancy When we approach an object or when it approaches us, we do not perceive it as getting larger. Even though the image of the object on the retina gets larger, we perceive this change as being due to a decrease in the distance between ourselves and the object. Our perception of the object’s size remains relatively constant. The unchanging perception of an object’s size and shape when it moves relative to us is called form constancy. Psychologists also refer to size constancy, but size is simply one aspect of form. In the nineteenth century, Hermann von Helmholtz suggested that form constancy was achieved by unconscious inference, a mental computation of which we are unaware. We know the size and shape of a familiar object. Therefore, if the image it casts upon our retina is small, we perceive it as being far away; if the image is large, we perceive it as being close. In either case, we perceive the object itself as being the same size. Form constancy also works for rotation. The drawing in Figure 6.34 (a) could be either a trapezoid or a rectangle rotated away from us. However, the extra cues clearly identify the drawing in Figure 6.34 (b) as a window, and experience tells us that windows are rectangular rather than trapezoidal; thus, we perceive it as rectangular. Obviously, this effect will not be seen in members of cultures that do not have buildings fitted with rectangular windows (or seen by people unfamiliar with the object).
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Figure 6.34 Form constancy. (a) This figure can be perceived as a trapezoid. (b) Because we recognise this figure as a window, we perceive its shape as rectangular.
The process just described works for familiar objects. However, we often see unfamiliar objects whose size we do not already know. If we are to perceive the size and shape of unfamiliar objects accurately, we must know something about their distance from us. An object that produces a large retinal image is perceived as big if it is far away and small if it is close. Figure 6.35 illustrates this phenomenon. Although the two letterboxes are exactly the same size, the one that appears to be further away looks larger. If you turn the book upside-down and look at the figure again, the appearance of depth is greatly diminished, and the two letterboxes appear to be approximately the same size.
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Detection of movement is one of the most primitive aspects of visual perception (Milner and
Figure 6.35 Effect of perceived distance. Although both letterboxes are exactly the same size, the upper one looks larger because of the depth cues (perspective and texture) that surround it. If you turn the book upside-down and look at the picture, thus disrupting the depth cues, the letterboxes look the same size.
Goodale, 1995). This ability is seen even in animals whose visual systems do not obtain detailed images of the environment. Of course, our visual system can detect more than the mere presence of movement. We can see what is moving in our environment and can detect the direction in which it is moving.
Adaptation and long-term modification One of the most important characteristics of all sensory systems is that they show adaptation and rebound effects. For example, when you stare at a spot of colour, the adaptation of neurons in your visual system will produce a negative after-image if you shift your gaze to a neutral background; and if you put your hand in some hot water, warm water will feel cool to that hand immediately afterwards.
Cutting edge – Content over style? When we see a work of art, what do we perceive first – the content, the style, the colour? A new development in the study of art perception is microgenesis – the process whereby our perception of art can be broken down into sub-types of perception, each varying in complexity. For example, which perceptual features are necessary for us to identify an image presented for 1 ms or 50 ms? Researchers from the University of Salzburg and Vienna used this technique to examine the point at which people were able to distinguish between two works of art that varied in style or content (Augustin et al., 2008). The researchers pre-
sented participants with two images on a computer monitor and asked them how similar they were. The images varied according to content (trees, flowers, houses, men/boys) and style (Cezanne, Chagall, Kirchner, Van Gogh). Presentation times were 10, 50, 202 and 3,000 ms. The time taken to make the judgement was recorded. Participants were able to distinguish between content at all presentation times, but effects of style became apparent at 50 ms. That is, participants were able to distinguish between works of art of different styles even when presented for only 50 ms, despite having no prior education in art.
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Motion, like other kinds of stimuli, can give rise to adaptation and after-effects. Tootell et al. (1995) presented participants with a display showing a series of concentric rings moving outwards, like the ripples in a pond. When the rings suddenly stopped moving, participants had the impression of the opposite movement – that the rings were moving inwards. During this time, the experimenters scanned the participants’ brains to measure their metabolic activity. The scans showed increased activity in the motion-sensitive region of the visual association cortex, which lasted as long as the illusion did. Thus, the neural circuits that give rise to this illusion appear to be located in the same region that responds to actual moving stimuli.
Interpretation of a moving retinal image As you read this book, your eyes are continuously moving. Naturally, the eye movements cause the image on your retina to move. You can also cause the retinal image to move by holding the book close to your face, looking straight ahead, and moving it back and forth. In the first case, when you were reading normally, you perceived the book as being still. In the second case, you perceived it as moving. Why does your brain interpret the movement differently in these two cases? Try another demonstration. Pick a letter on this page, stare at it, and then move the book around, following the letter with your eyes. This time you will perceive the book as moving, even though the image on your retina remains stable. Thus, perception of movement requires coordination between movements of the image on the retina and those of the eyes. Obviously, the visual system must know about eye movements in order to compensate for them in interpreting the significance of moving images on the retina. Another simple demonstration suggests the source of this information. Close your left eye and look slightly down and to the left. Gently press your finger against the outer corner of the upper eyelid of your right eye and make your right eye move a bit. The scene before you appears to be moving, even though you know better. This sensation of movement occurs because your finger – not your eye muscles – moved your eye. When your eye moves normally, perceptual mechanisms in your brain compensate for this movement. Even though the image on the retina moves, you perceive the environment as being stationary. However, if the image moves because the object itself moves or because you push your eye with your finger, you perceive movement (see Figure 6.36). In general, if two objects of different size are seen moving relative to each other, the smaller one is perceived as moving and the larger one as standing still. We perceive people at a distance moving against a stable background and flies moving against an unmoving wall. Thus, when an experimenter moves a frame that encloses
Command to move eyes
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Eye muscles Comparison between eye movement and movement of image on retina Retina Perception of movement
Figure 6.36 A schematic representation of the brain mechanisms responsible for the interpretation of a moving retinal image. This system must compensate for eye movements.
a stationary dot, we tend to see the dot move, not the frame. This phenomenon is also encountered when we perceive the moon racing behind the clouds, even though we know that the clouds, not the moon, are moving. Perception of movement can even help us perceive threedimensional forms. Johansson (1973) demonstrated just how much information we can derive from movement. He dressed actors in black and attached small lights to several points on their bodies, such as their wrists, elbows, shoulders, hips, knees and feet. He made films of the actors in a darkened room while they were performing various behaviours, such as walking, running, jumping, limping, doing push-ups, and dancing with a partner who was also equipped with lights. Even though observers who watched the films could only see a pattern of moving lights against a dark background, they could readily perceive the pattern as belonging to a moving human and could identify the behaviour the actor was performing. Subsequent studies (Kozlowski and Cutting, 1977; Barclay et al., 1978) showed that people could even tell, with reasonable accuracy, the sex of the actor wearing the lights. The cues appeared to be supplied by the relative amounts of movement of the shoulders and hips as the person walked.
Combining information from successive fixations As Chapter 5 showed, when examining a scene, our eyes do not roam slowly around; rather, they make rapid steplike movements called saccades. After each saccade, the eyes rest for a while, gathering information before moving again. These stops are called fixations. The visual system combines the information from each fixation and perceives objects too large or too detailed to see in a single glance. Obviously, in doing so, it must keep track of the locations of each of the fixations. Figure 6.37 (a) illustrates an impossible object. At first glance, the lines represent a three-dimensional object. However, careful inspection shows that the object cannot
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You can read You this can sentence read this clearly sentence clearly (a) if material from every fixation pause were retained during the later fixation pauses, a sentence might look like this at the third fixation pause. You can read this sentence clearly (b) Fortunately, masking prevents the persistence of earlier material, and so we see a sentence that looks like this.
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Figure 6.38 The role of backward masking. If each saccade did not erase the remaining image from the previous fixation, we probably would not be able to read. Source: From Margaret W. Matlin and Hugh H.J. Foley, Sensation and Perception, 3rd edn © 1992. Published by Allyn & Bacon, Boston, MA. Copyright © by Pearson Education. By permission of the publisher.
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Figure 6.37 (a) An impossible figure. Only after carefully studying the figure do we see that it cannot be a drawing of a real threedimensional object. (b) An unconvincing impossible figure. When the legs are short enough so that the entire figure can be perceived during a single fixation, the figure does not look paradoxical.
possibly exist. But the drawing in Figure 6.37 (b) creates a very different impression; it does not look at all like a unified three-dimensional object. The difference in the two impressions is that the details of the larger figure cannot be gathered in a single glance. Apparently, when we look from one end of the figure to the other, the information we gather from the first fixation is slightly modified to conform to the image of the second one. Of course, the two images do not exactly match, as a careful inspection shows. Clearly, what we see during one fixation affects what we see in another. If two visual stimuli are presented, one after the other, the second stimulus could sometimes erase the image of the first. That is, under the appropriate conditions, the subject would fail to perceive the image that came first. This phenomenon is known as backward masking (Werner, 1935).
Normally, backward masking can be demonstrated only in the laboratory, where the shape and intensity of the stimuli and the time interval between them can be carefully controlled. Breitmeyer (1980) suggests that the explanation for this phenomenon lies in the nature of the saccadic movements made by the eyes when gathering information about the visual environment. For example, consider the saccadic movements that your eyes make as you read a line of text in this book. You do not stop and look at each letter or even at each word; instead, you make several fixations on each line. During each one, your visual system gathers information and begins decoding the letters and words. Your eyes move on, and you perceive more words. Breitmeyer suggests that each saccade erases the image remaining from the previous fixation, leaving only the information that has been analysed by the visual system. Figure 6.38 illustrates what might happen if this erasure did not occur.
A good science tries to create theories that apply generally to most contexts, events or people. In psychology’s case, a good theory should apply to all people. However, there are instances where group differences test this assumption, such as when cultures are compared across some variable. For example, there is a small amount of evidence to suggest that differences in visual perception exist between Western people and those from East Asia – Westerners tend to perceive objects more analytically and in a more focused way; East Asians are more likely to attend to the context in which objects appear (i.e. they perceive a scene ‘holistically’) (Choi and Nisbett, 1998; Chua et al., 2005a).
In one study where American and Japanese participants were asked to describe an underwater scene, Americans were more likely to describe objects in the water but the Japanese reported 60 per cent more information about the background environment (Masuda and Nisbett, 2001). In a different scenario, Americans were also able to identify an object (a tiger) more accurately than were the Japanese when it appeared against a different background from that in which it was originally seen. Why does this focal v. context effect occur? One reason might be the types of eye movement made by different cultures. To test this hypothesis, Chua et al. (2005) asked American and Chinese participants to view scenes in which objects
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The psychology of art – An international perspective Different nations and different cultures as well as groups within those nations and cultures produce art that can be as similar as it is different. Researchers, however, have found significant differences in the art and artistic depictions of people from the East and the West. In one study, Masuda et al. (2008) analysed the artistic styles in art sourced from the archives of various museums. A total of 365 Western and 218 Eastern landscapes were analysed and 286 and 151 portrait paintings from these cultures were compared. Eastern landscape art was more likely to place the horizon higher than was Western art. This creates more space for field information. For portrait paintings, the size of the models was smaller in the Eastern sample – the Western sample was less likely to include more background. In a second study, groups of American and Taiwanese, Korean, Japanese and Chinese students were asked to draw and photograph landscapes and portraits. The use of context was greater in both types of stimuli in the Eastern sample. It was more likely to draw the horizon in a high position and draw more objects. It was also more likely to use the zoom function to minimise the size of the model in portrait photographs and make the context larger.
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If you sit in a darkened room and watch two small lights that are alternately turned on and off, your perception will be that of a single light moving back and forth between two different locations. You will not see the light turn off at one position and then turn on at the second position. If the distance and timing are just right, the light will appear to stay on at all times, quickly moving between the positions. This
response is known as the phi phenomenon. ‘Moving’ neon signs and some computer animations make use activit ee of it. This characteristic of the visual system yp sych accounts for the fact that we perceive the images in cinema films, video tapes and television as continuous rather than separate. The images actually jump from place to place, but we see smooth movement. s
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Similar cultural effects can occur when rating facial expressions. Participants in one experiment were asked to rate the degree of emotion shown in cartoons depicting happy, sad, angry or neutral facial expressions. These faces were surrounded by other people expressing the same or different emotion (Masuda et al., 2008). The surrounding stimuli influenced the ratings of Japanese participants significantly more than they did Westerners. This was evidenced by eye-tracking data. The Japanese spent more time looking at the surrounding stimuli than did the Westerners. The lack of self-absorption of Japanese participants was also seen in an experiment in which people completed a verbal fluidity task – where there was an opportunity to cheat – in front of a mirror (Heine et al., 2008). North Americans were more self-critical and less likely to cheat in front of the mirror; the Japanese participants were unaffected by the presence of a mirror.
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appeared against complex backgrounds. The eye movement of participants as they viewed the object and scene were then tracked. Compared with the Chinese, Americans focused on specific objects and more quickly. The Chinese made more saccades – eye movements – to the background. The researchers suggest that this effect could partly be explained by socialisation. East Asians grow up and live in complex social networks in which paying attention to context is important (perhaps more important than focusing on individual objects or people); Westerners, however, are educated to value individuality and independence (and eye movement is, therefore, directed accordingly). This extends even to cultural products. An analysis of advertising and popular texts in Western and Asian (Korea, Japan, China)/Mexican cultures found that the latter were more individualistic and less collectivistic (Morling and Lamoreaux, 2008).
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Finally, American and East Asians students were asked to rate their preference for portrait photographs where the model and the background varied. Japanese participants were significantly less likely to prefer narrow backgrounds and larger models. The findings are consistent with those of other studies. Miyamoto et al. (2006) took photographs of significant cultural institutions in the US and Japan. These included schools, post offices, hotels, etc. The institutions in Japan featured more objects and were visually more complex. Why do these differences occur? Masuda et al. (2008) cite Cohen et al’s insider/outsider view of how we organise information about the world (Cohen and Gunz, 2002; Cohen et al, 2007). The insider is dominant in the West – this person dwells on his/her own private experiences and sees the world from his/her point of view. The outsider views the world from the point of view of an outsider looking at the self. It seems as if these roles can change. For example, people who have been exposed to Japanese scenes for a few minutes notice more context than those who are exposed to American scenes (Miyamoto et al., 2006).
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Brain mechanisms of visual perception
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Although the eyes contain the photoreceptors that detect areas of different brightnesses and colours, perception takes place in the brain. As you saw in Chapters 4 and 5, the optic nerves send visual information to the thalamus, which relays the information to the primary visual cortex located in the occipital lobe at the back of the brain. In turn, neurons in the primary visual cortex send visual information to two successive levels of the visual association cortex. The first level, located in the occipital lobe, surrounds the primary visual cortex. The second level is divided into two parts, one in the middle of the parietal lobe and one in the lower part of the temporal lobe. Figure 6.39 illustrates the various regions involved in visual perception. Visual perception by the brain is often described as a hierarchy of information processing. According to this scheme, circuits of neurons analyse particular aspects of visual information and send the results of their analysis on to another circuit, which performs further analysis. At each
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Figure 6.39 The visual system of the brain. Arrows represent the flow of visual information. Sensory information from the eye is transmitted through the optic nerve to the thalamus, and from there it is relayed to the primary visual cortex. The results of the analysis performed there are sent to the visual association cortex of the occipital lobe (first level) and then on to that of the temporal lobe and parietal lobe (second level). At each stage, additional analysis takes place.
step in the process, successively more complex features are analysed. Eventually, the process leads to the perception of the scene and of all the objects in it. The higher levels of the perceptual process interact with memories: the viewer recognises familiar objects and learns the appearance of new, unfamiliar ones. Deprivation of the visual system or damage to it during the early years of development can have significant consequences for visual function.
The primary visual cortex Our knowledge about the characteristics of the earliest stages of visual analysis has come from investigations of the activity of individual neurons in the thalamus and primary visual cortex. For example, Hubel and Wiesel inserted microelectrodes – extremely fine wires having microscopically sharp points – into various regions of the visual system of cats and monkeys to detect the action potentials produced by individual neurons (Hubel and Wiesel, 1977, 1979). The signals detected by the microelectrodes are electronically amplified and sent to a recording device so that they can be studied later. After positioning a microelectrode close to a neuron, Hubel and Wiesel presented various stimuli on a large screen in front of the anaesthetised animal. The anaesthesia makes the animal unconscious but does not prevent neurons in the visual system from responding. The researchers moved a stimulus around on the screen until they located the point where it had the largest effect on the electrical activity of the neuron. Next, they presented the animal with stimuli of various shapes in order to learn which ones produced the greatest response from the neuron. From their experiments, Hubel and Wiesel (1977, 1979) concluded that the geography of the visual field is retained in the primary visual cortex. That is, the surface of the retina is ‘mapped’ on the surface of the primary visual cortex. However, this map on the brain is distorted, with the largest amount of area given to the centre of the visual field. The map is actually like a mosaic. Each piece of the mosaic (usually called a module) consists of a block of tissue, approximately 0.5 ⫻ 0.7 mm in size and containing approximately 150,000 neurons. All of the neurons within a module receive information from the same small region of the retina. The primary visual cortex contains approximately 2,500 of these modules. Because each module in the visual cortex receives information from a small region of the retina, that means that it receives information from a small region of the visual field – the scene that the eye is viewing. If you looked at the scene before you through a straw, you would see the amount of information received by an individual module. Hubel and Wiesel found that neural circuits within each module analysed various characteristics of
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their own particular part of the visual field, that is, of their receptive field. Some circuits detected the presence of lines passing through the region and signalled the orientation of these lines (that is, the angle they made with respect to the horizon). Other circuits detected the thickness of these lines. Others detected movement and its direction. Still others detected colours. Figure 6.40 shows a recording of the responses of an orientation-sensitive neuron in the primary visual cortex. This neuron is located in a cluster of neurons that receive information from a small portion of the visual field. That is, the neuron has a small receptive field. The neuron responds when a line oriented at 50 degrees to the vertical is placed in this location – especially when the line is moving through the receptive field. This response is specific to that orientation; the neuron responds very little when a line having a 70-degree or 30-degree orientation is passed through the receptive field. Other neurons in this cluster share the same receptive field but respond to lines of different orientations. Thus, the orientation of lines that pass through this receptive field is signalled by an increased rate of firing of particular neurons in the cluster. Because each module in the primary visual cortex receives information about only a restricted area of the visual field, the information must be combined somehow for perception to take place. This combination takes place in the visual association cortex.
Experimenter moves black bar through receptive field at various angles
How different are imagining and perceiving visual stimuli? Does visual imagery use the same brain areas as those involved in visual perception? Does the imagining of different types of ‘mental’ content activate different brain areas and if so, are they areas that would be normally activated by the actual perception of such content? Would imagining faces, for example, activate the same area(s) as that or those activated by the viewing of actual faces? In one study, functional Magnetic Resonance Imaging was used to determine whether the brain areas activated during the mental imagining of faces were similar to or different from those activated during the mental imagining of places (O’Craven and Kanwisher, 2000). A region at the back of the brain, the human fusiform face area (HFFA), was significantly more active during the mental imagining of faces than places. They also found that imagining places activated a region called the parahippocampal place area (PPA) to a much greater extent than did the faces (as for the HFFA, the PPA becomes active when people look at places). Both of these regions can be seen in Figures 6.41. These results are similar to those obtained by Goebel et al. (1998), who found that the brain region activated during visual motion was also activated during the mental imagery of motion. Studies at the level of individual
Receptive field of neuron whose activity is being recorded
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Figure 6.40 Responses of a single neuron to lines of particular orientations that are passed through its receptive field.
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Human fusiform gyrus (human face area)
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Figure 6.41 The parahippocampal place area (a) and the fusiform face area (b) of the brain.
groups of cells also show overlap in activation during actual perception and imagination. Kreiman et al. (2000), for example, recorded electrical activity from 276 neurons from the lateral (side) regions of the brain (the medial temporal lobes) as participants imagined previously viewed faces, objects, spatial layouts and animals. The purpose of the experiment was to determine whether the same neurons would respond when viewing images as when imagining them. As predicted, the authors found that when neurons responded selectively to a stimulus (that is, responded to that stimulus but not to another, indicating that the response is stimulus-specific), the same neurons were active whether the person viewed or imagined the stimulus. There was a great deal of overlap between neural response during actual viewing and imagining what was viewed. These studies suggest that the mechanisms responsible for visual perception of images and those responsible for the mental imagining of the same images are similar. The mechanisms may be shared – the results from O’Craven and Kanwisher’s study (2000), for example, suggest that the difference in activation between the two types of condition (imagery v. viewing) was one of degree, rather than type.
The visual association cortex The first level of the visual association cortex, which surrounds the primary visual cortex, contains several subdivisions, each of which contains a map of the visual scene. Each subdivision receives information from different types of neural circuit within the modules of the
primary visual cortex. One subdivision receives information about the orientation and widths of lines and edges and is involved in perception of shapes. Another subdivision receives information about movement and keeps track of the relative movements of objects (and may help compensate for movements of the eyes as we scan the scene in front of us). Yet another subdivision receives information concerning colour (Zeki, 1993; Milner, 1998). You can see these subdivisions in Figure 6.42. The two regions of the second level of the visual association cortex put together the information gathered and processed by the various subdivisions of the first level. Information about shape, movement and colour are combined in the visual association cortex in the lower part of the temporal lobe. Three-dimensional form perception takes place here. The visual association cortex in the parietal lobe is responsible for perception of the location of objects. It integrates information from the first level of the visual association cortex with information from the motor system and the body senses about movements of the eyes, head and body. Researchers have studied the anatomy and functions of the visual association cortex in laboratory animals. Neuroimaging studies have also been used to locate comparable subregions in humans. For example, when a person looks at a display containing irregular patches of different colours, one region of the visual association cortex becomes active. When a person looks at a display of moving blackand-white squares, another region becomes active (see Figure 6.43). Presumably, these areas are involved in the analysis of colour and movement, respectively.
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Visual scene is broken into modules; information is analysed in terms of orientation, thickness of lines, colour, movement, etc.
Movement
Information from both eyes Eye
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Thalamus
Second level of association cortex in parietal lobe Perception of location and movement Second level of association cortex in temporal lobe
Orientation and widths of lines Three-dimensional form perception Colour
Figure 6.42 Schematic diagram of the types of analysis performed on visual information in the primary visual cortex and the various regions of the visual association cortex.
Brain damage and visual perception ee
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Research with laboratory animals and data from individuals with brain damage have shown that yp sych certain areas of the visual cortex, the lingual and fusiform gyri, are important for discriminating between colours (Damasio et al., 1980; Davidoff, 1997). Damage h syc la
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to this area causes achromatopsia, a form of colour blindness in which the world is seen in shades of grey, as Figure 6.44 shows. Neuroimaging studies also suggest that these areas are active in healthy individuals during a simple task where participants perceive colours (McKeefry and Zeki, 1997). McKeefry and Zeki suggest that there is an area or areas outside the primary visual cortex – V4, in the ventral occipitotemporal cortex – which mediates colour perception.
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Figure 6.43 PET scans of the human brain showing regions of increased metabolic activity (indicating increased neural activity) when the subjects looked at multicoloured patterns (a) and moving black and white rectangles (b). Source: Adapted from Zeki, S., La Recherche, 1991, 21, 712–21.
Figure 6.44 A photograph illustrating the way the world would look to a person who had achromatopsia in the right visual field, caused by damage on the left side of the brain to the region of the visual association cortex.
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The finding that damage to different parts of the visual system results in different types of impairment in visual perception suggests that some visual system pathways carry one type of information whereas others carry different types of information. Schneider (1969) had proposed that there were two major visual system pathways: a geniculostriate pathway which was responsible for identifying stimuli and discriminating between patterns, and a retinotectal pathway which was responsible for locating objects in space. Schneider’s theory has since been modified, although the idea that different brain regions are responsible for the perception of an object’s qualities and its location is valid. Ungerleider and Mishkin (1982), for example, have suggested that different parts of the brain are involved in object identification and object location: the appreciation of an object’s qualities is the role of the inferior temporal cortex; the ability to locate an object is the role of the posterior parietal cortex. Primates with posterior parietal cortex lesions make consistent errors in accurately reaching out for or grasping objects although their ability to discriminate between objects is intact. Similar damage in humans also results in difficulties performing visuospatial tasks such as estimating length and distance (Von Cramon and Kerkhoff, 1993; Jeannerod et al., 1994). Recall from Chapter 4 that the parietal cortex plays an important role in visually guiding movement and in grasping or manipulating objects (Sakata, 1997). Importantly, Ungerleider and Mishkin distinguished between a ventral and dorsal pathway or stream which projected from the primary visual cortex (PVC) to these areas. Thus, although originating in the PVC, the two pathways were independent and projected to different areas of the brain (to the temporal and posterior parietal cortices, respectively).
Dorsal stream
Primary visual cortex
Ventral stream
Figure 6.45 The two visual routes (ventral and dorsal) and their pathway from the visual cortex. Source: From Pinel, John P.J., Biopsychology, 3rd edn © 1997. Published by Allyn & Bacon, Boston, MA. Copyright Pearson Education.
Goodale and Milner (1992; Milner and Goodale, 1995) developed the theory further. What is important, they argue, is not ‘what’ and ‘where’, but ‘what’ and ‘how’. In Ungerleider and Mishkin’s model, the ventral stream processes the ‘what’ component of visual perception (identification of an object) whereas the dorsal stream processes the ‘where’ component (the spatial location of an object). Goodale and Milner’s research has focused on the ‘what’ and ‘how’ areas. The brain regions representing these streams can be seen in Figure 6.45. Goodale and Milner have made an extensive study of DF, a woman with substantial bilateral damage to the occipital cortex (but sparing the PVC) resulting from carbon monoxide poisoning (Goodale and Milner, 1992; Milner and Goodale, 1995). DF is unable to discriminate between geometric shapes and is unable to recognise or identify objects, despite having no language or visual sensory impairment (Milner et al., 1991). That is, she exhibits visual form agnosia (agnosia is described in more detail in the next section). DF is able to respond to objects. For example, she can place her hand into a slot of varying orientations or grasp blocks (Goodale et al., 1991). However, when she is asked to estimate the orientation of the slot or the width of the box by verbally reporting or by gesturing, she is unable to do so. Why? DF may be using the intact visuomotor processing system in the parietal cortex to perform the grasping and orientation tasks (Milner and Goodale, 1995; Milner, 1998). The guidance of motor behaviour relies on a primitive dorsal stream in the parietal cortex which is spared in DF. This is why the execution of her motor behaviour is accurate. When asked to indicate which of two boxes is a rectangle and which is a square, she can respond correctly when holding the boxes but less correctly when making a verbal response (Murphy et al., 1996). DF would make partial movements towards one of the boxes before correcting herself. When these initial reaches were analysed, they showed the same level of accuracy as if she had verbally reported which box was which. Did DF monitor the size of her anticipatory grip before making a decision? There is evidence that she does. When asked to look at a series of lines of varying orientation and then copy them on a separate piece of paper, DF would outline the line in the air before making a copy. When asked not to do this, her copies were still relatively accurate. She found the task easier if she imagined herself drawing the line: when she was asked to copy the line immediately – thereby preventing rehearsal from taking place – she failed (Dijkerman and Milner, 1997). DF must have generated a motor image of the lines to allow her to accomplish this task, a behaviour which would have been made possible by intact functioning of the frontal and parietal lobes. On the basis of DF’s behaviour, research from neuroimaging studies of motor movement and vision, and animal lesions to parietal and occipital areas, Milner and
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Goodale (1995) propose that the dorsal stream sends information about object characteristics and orientation that is related to movement from the primary visual cortex to the parietal cortex. Damage to the ventral stream, which projects to the inferior temporal cortex, is what is responsible for DF’s inability to access perceptual information.
Projections to the primary visual cortex Two specific cellular pathways – the parvocellular (P) and magnocellular (M) pathways – run from the retina to the cortex and terminate in different layers of the primary visual cortex (V1). Other layers of V1 project to other dorsal and ventral stream areas. Layers 2 and 3 of V1, for example, provide input to the ventral stream areas whereas layer 4B sends input to dorsal stream areas. Layer 4B also receives input from the M and P pathways and projects to areas such as V5, a region known to be involved in motion perception. Many other circuits such as this are made within the visual system but comparatively little is known about how functionally relevant such connections are or how different types of cell contribute to the circuitry. One study has shown that different types of neurons in area V1 receive different signals from the M and P pathways and forward this information to other specific cortical areas (Yabuta et al., 2001). The results of the study suggest that if two types of cell project to different layers, perhaps each type carries different types of information in the cortical visual system.
Perceptual disorders When the brain is damaged and visual perception is impaired, the patient is said to exhibit a perceptual disorder. There are several perceptual disorders and each is associated with damage to different parts of the visual system. It is important to note that these disorders are strictly perceptual, that is, there is no underlying impairment in sensation (patients retain visual acuity and the ability to tell light from dark and so on). The basic visual sensory system itself is, therefore, unimpaired. Three of the most important perceptual disorders are blindsight, agnosia and spatial neglect. Each is important in its own way because they demonstrate how brain damage can affect different aspects of visual perception.
Blindsight When the primary visual cortex is damaged, a person becomes blind in some portion of the visual field. Some individuals, however, can lose substantial areas of the PVC and yet show evidence of perceiving objects despite being ‘cortically blind’. This phenomenon is called blindsight (Weiskrantz, 1986, 1997) because although patients are unable to see properties of objects they are aware of other
aspects such as movement of objects. Moving objects are better detected than still ones, objects can be located if they are pointed at and they can detect movement and colour, despite being ‘unable’ to see the stimuli. (There are equivalent phenomena in the auditory and somatosensory systems called deaf hearing and blindtouch.) The earliest case of blindsight was reported at the beginning of the last century (Riddoch, 1917). Riddoch was an army medical officer who had made a study of soldiers whose primary visual cortex had been damaged by gunshot wounds. Although none of the patients could directly describe objects placed in front of them (neither shape, form nor colour), they were conscious of the movement of the objects, despite the movement being ‘vague and shadowy’. This suggested to Riddoch that some residual visual ability in the PVC remained which allowed the perception of object motion but no other aspect of visual perception. Some patients need to be prompted to ‘guess’ (Blindsight Type 1) whereas others will reports vague sensations (Blindsight Type 2) although both types claim that they cannot see anything. That the PVC is damaged led to the hypothesis that this area was responsible for conscious visual perception (Radoeva et al., 2008). Since Riddoch’s study, several other cases of blindsight have been reported, notably Larry Weiskrantz’s famous patient, DB (Weiskrantz, 1986). DB had undergone surgery for a brain tumour, which necessitated removal of the area of the visual cortex in the right occipital lobe. This surgery resulted in a scotoma – an area of complete blindness in the visual field. DB could indicate whether a stick was horizontal or vertical, could point to the location of an object when instructed, and could detect whether an object was present or absent. Other tasks presented greater difficulty: DB could not distinguish a triangle from a cross or a curved triangle from a normal one. The most intriguing feature of DB’s behaviour, however, was a lack of awareness of the stimuli presented. According to DB, he ‘couldn’t see anything’ when test stimuli were seen. Why could DB, and patients like DB, make perceptual decisions despite being unaware of visual stimuli? One hypothesis suggests that perceptual tasks can be completed successfully because stray light emitted by stimuli makes its way from the intact field of vision because it reflects from surfaces outside the eye area – what is called extraocular scatter. Cowey (2004) has suggested that one way of controlling for this light scatter is to mask the blind field from view by placing a half-patch over the viewing eye, but this control is rarely employed. There can also be an intraocular source of light scatter – according to Cowey (2004), visual stimuli always ‘smear’ the retina. Because stimuli in blindsight studies have been presented very close to the eye, this has allowed the retina to be smeared with the image and to be stimulated, leading to crude visual perception.
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The stray light hypothesis, however, appears to be an unlikely explanation because DB is able to make perceptual decisions in the presence of strong ambient light which reduces the amount of stray light emitted by stimuli. More to the point, this theory does not explain how DB can still make decisions based on the spatial dimensions of objects. An alternative hypothesis suggests that the residual perceptual abilities of patients such as DB are attributable to the degrading of normal vision, possibly due to the presence of some residual striatal cortex (‘islands’ of PVC cortex that are undamaged) (Scharli et al., 1999; Wessinger et al., 1999). Implicit in this hypothesis is the notion that residual abilities are not attributable to the functioning of another visual system pathway. There are ten known pathways from the retina to the brain (Stoerig and Cowey, 1997). As you have seen, there appear to be two distinct pathways in the visual system which mediate different aspects of vision. The visual location of objects, for example, is thought to be a function of a system which includes the superior colliculus, the posterior thalamus and areas 20 and 21, whereas the analysis of visual form, pattern or colour is thought to be a function of the geniculostriate system which sends projections from the retina to the lateral geniculate nucleus, then to areas 17, 18 and 19, and then to areas 20 and 21. Blindsight could, therefore, conceivably be due to a disconnection between these two systems. Again, there are arguments against this hypothesis. Curiously, DB, although unable to ‘see’ objects when presented to him – even 30 years after his deficit was first studied, appears to be aware of a visual ‘after-image’ after a stimulus on a monitor is switched off (Weiskrantz et al., 2002). The colour and spatial structure of the stimulus can be described, a phenomenon that is correlated with increased prefrontal cortex activity (Weiskrantz et al., 2003). It is unclear whether this ability is due to spared striate cortex, however, because DB has surgical clips which prevent him from undergoing an MRI scan which would demarcate the preserved cortex. Another patient, GY, has no spared striate cortex, but still exhibits signs of blindsight (Azzopardi and Cowey, 2001). When the visual cortex of blindsight patients with spared striate cortex is imaged, there is no activation observed to visual stimuli that produce the blindsight phenomenon (Storeig et al., 1998). Both lines of evidence suggest that the spared striate cortex explanation is weak (although not completely dismissible – perhaps the degree and type of spared cortex are the important factors). What seems reasonable, but for which there is no hard evidence, is the hypothesis that blindsight relies on a primitive, early visual system that is not dependent on the striate cortex. A note of caution should be struck, however. Blythe et al. (1987), for example, found only 5 cases of blindsight in a sample of 25 patients; Marzi et al. (1986) found a similar ratio (4 patients out of 20) in their sample. The degree of variability in the appearance of
blindsight following striatal removal, therefore, suggests some restraint in extrapolating from individual cases.
Visual agnosia Patients with posterior lesions to the left or right hemisphere sometimes have considerable difficulty in recognising objects, despite having intact sensory systems. We saw an example of this in an earlier section when we discussed the perceptual impairments seen in patient DF. This disorder is called agnosia (literally ‘without knowledge’), a term coined by Sigmund Freud. Agnosia can occur in any sense (tactile agnosia refers to the inability to recognise an object by touch, for example) but visual agnosia is the most common type (Farah, 1990; Farah and Ratcliff, 1994). The existence of specific types of agnosia is a controversial topic in perception and neuropsychology. A distinction is usually made between two types of visual agnosia: associative and apperceptive. Apperceptive agnosia is the inability to recognise objects whereas associative agnosia is the inability to make meaningful associations to objects that are visually presented. Some neuropsychologists have argued that the boundaries between these two types are ‘fuzzy’ (DeRenzi and Lucchelli, 1993), and other sub-types of visual agnosia have been suggested (Humphreys and Riddoch, 1987a). Apperceptive agnosics have a severe impairment in the ability to copy drawings, as patient DF did. Associative agnosics, conversely, can copy accurately but are unable to identify their drawings. For example, Humphreys and Riddoch’s patient, HJA, spent six hours completing an accurate drawing but was unable to identify it when he had finished. Figure 6.46 shows you an example of HJA’s drawings.
Figure 6.46 The drawing of a building by HJA reflects great attention but he was unable to name it. The line drawings beneath are of very simple objects but HJA was unable to name them. Source: Humphreys and Riddoch (1987). To See or Not to See. Andover: Psychology Press, reprinted by permission of Thomson Publishing Services.
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There has been considerable debate concerning the specificity of visual object agnosia, that is, whether some patients are able to recognise some categories of object but not others (Newcombe et al., 1994). The commonest dissociation is seen between living and non-living things. Generally, it has been found that recognition of living objects (such as animals) is less accurate in agnosic patients than is recognition of non-living objects (Warrington and Shallice, 1984; Silveri et al., 1997). To determine whether different brain regions were responsible for this dissociation, Martin et al. (1996) conducted a PET study of healthy individuals’ brain activity as the subjects named pictures of tools or animals. Both categories of words were associated with activation in the visual cortex and Broca’s area (because the participants saw and spoke) but some areas were activated by the naming of animals (left occipital region) and others by the naming of tools (right premotor regions). Some psychologists, however, have argued that these studies do not show differences between the categories of object but between the ways in which these two different types of stimulus are presented. Parkin and Stewart (1993), for example, have suggested that it is more difficult to recognise drawings of animate than inanimate objects. An inanimate object such as a cup, is a lot less detailed than an animate object, such as a fly. The dissociation seen in agnosic patients, therefore, may be due to the complexity and/or familiarity of the perceived stimulus. Stewart et al. (1992) have suggested that when these artefacts are controlled for, these dissociations disappear. However, the issue continues to be controversial. Sheridan and Humphreys (1993), for example, have shown that patients show such dissociations even under well-controlled conditions and a recent review suggests that specific brain regions may mediate the recognition of objects from different semantic categories (Gainotti, 2000).
Prosopagnosia A more category-specific form of agnosia is prosopagnosia. Some individuals with damage to specific areas of the posterior right hemisphere (and sometimes left and right hemispheres) show an impairment in the ability to recognise familiar faces. This condition is known as prosopagnosia (‘loss of knowledge for faces’). Some patients are unable to recognise famous faces (Warrington and James, 1967) or familiar people such as spouses (DeRenzi, 1986). This disorder, while rare, can have dramatic effects on a person’s everyday life. For example, here are some comments from patients with prosopagnosia on how their condition affects them (all from Yardley et al., 2008):
“I was getting off a bus and somebody got on it and grabbed me, and I pushed them out of the way and it was only when they opened their mouth that I realized it was my own mother.” “Sometimes if I see someone and I’m not sure if I know them I just try and keep out of their way and hope they don’t see me, ’cause I don’t know how to act.” “The condition makes me less interested in the social events, the partying, the getting to know lots of people, because that just gives me a whole set of things I’ll get wrong.” “I’d try, spend three days chatting up some girl and then cut her dead in the street without knowing that I’d done it.”
Barry Wainwright, who suffers from prosopagnosia: ‘If I look at a photograph of myself, I don’t know it’s me. I don’t recognise my wife or my seven children, either, even when I’m looking right at them.’ Source: From The Guardian Weekend Magazine, 22 November 2008, p. 12.
Much of the recent neuropsychological work on face recognition has exploited neuroimaging techniques in order to determine whether different regions of the human brain respond to faces selectively. One controversy in the area surrounds whether such selective activation is specific to faces or to some other perceptual aspect of faces, such as whether they appear in greyscale or in two-tone. Kanwisher et al. (1998), for example, found that the brain region which you encountered in the earlier section, the human fusiform face area (HFFA), was significantly activated when people viewed upright and inverted greyscale faces. Inverted two-tone faces, however, were associated
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with significantly reduced brain activation. The results suggest that the HFFA does not respond specifically to low-level features of faces (if it did, the inverted and upright two-tone faces would have produced similar activation) but does respond to face stimuli. The authors acknowledge, however, that this may not be the only brain region specialised for face processing. Current neuroimaging data make HFFA a strong contender for the role of the brain’s primary face processor. Its response is stronger when viewing faces, followed by whole humans and animal heads (Kanwisher et al., 1999) and appears to be involved in remembering, as well as seeing, faces (Kuskowski and Pardo, 1999). GornoTempini et al. (1998) compared the human brain’s ability to process, implicitly or explicitly, famous and unknown face stimuli, proper names and object names and report that the perceptual analysis of faces was associated with selective activation of the HFFA in both hemispheres of the brain. Other regions were implicated in famous name processing (relative to common names). The same research group also reported a study in which activation to famous and non-famous faces and buildings was recorded (Gorno-Tempini and Price, 2001). In this experiment, they found that the HFFA and the PPA were selectively activated by faces and buildings, respectively, regardless of fame (although other regions were activated during exposure to the famous stimuli). One view, however, suggests that the FFA, rather than being specialised for recognising faces, is responsible for distinguishing between members of a homogeneous class of objects (not just faces). A related argument suggests that the FFA is active when it distinguishes between members of object classes that we are expert in identifying. Because we are very familiar with faces, and expert at recognising them, the FFA is, therefore, active when we view faces. This argument also suggests, however, that expert identifiers should activate the FFA when they view objects they are expert in recognising (and not just faces). To test these various hypotheses, Rhodes et al. (2004) set up two experiments in which people were either trained or were not trained to recognise Lepidoptera (moths and butterflies). Brain activation was monitored using fMRI while participants viewed faces and Lepidoptera. In the second experiment, experts in identifying moths and butterflies passively watched examples of the species while brain activity was recorded. If the FFA is active during expert discrimination, then it should be just as active during face perception and Lepidoptera perception in experts. The authors found no support for this hypothesis. In the first experiment, the FFA was more significantly activated when people watched faces than Lepidoptera, regardless of whether people had been trained to recognise examples of
the species. In the second experiment, activation was greater in the FFA when the butterfly experts watched faces than Lepidoptera. There was no overlap in the areas activated by faces and moths and butterflies. The results suggest that the FFA contains neurons that allow ‘individuation’ of (i.e. discrimination between) faces.
Spatial neglect Patients with lesions in the right parietotemporal cortex sometimes have difficulty in perceiving objects to their left (Vallar, 1998). In fact, in 80 per cent of patients with right hemisphere stroke, patients are unable to attend automatically to any stimuli in left space (Halligan and Marshall, 1994). This is called spatial neglect (or unilateral spatial hemineglect) and occurs on the side of the body that is contralateral to the side of the brain damage (the regions damaged can be seen in Figure 6.47). Neglect for the left side is more common than right neglect (which would be caused by damage to the left hemisphere). Patients exhibiting spatial neglect behave as if half of the world does not exist. They may forget to attend to their clothing on the left-hand side, neglect food on the left side of the plate or ignore the left-hand side of their newspaper (Halligan and Cockburn, 1993; Halligan and Marshall, 1994). Spatial neglect patients show a characteristic pattern of behaviour on visuospatial tests. For example, if they are required to bisect lines of varying length, they will err to the right. If they are presented with an array of stimuli (such as small lines) and asked to mark off as many as possible, they mark off those on the right-hand side but fail to mark off those on the left, as seen in Figure 6.48.
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Figure 6.47 The areas of the brain damaged in spatial neglect patients. Most patients have damage to region A; some can have damage to region B.
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Figure 6.49 The famous clock-drawing task at which spatial neglect patients are impaired. Patients either neglect the numerals on the left side completely or bunch them up on the right.
Figure 6.48 The line cancellation task. Spatial neglect patients consistently neglect one side of the display (in this example, the left side).
Similarly, neglect patients, when asked to draw (or mentally imagine a scene) fail to draw or report details from the left side of the object or image (Halligan and Marshall, 1994; Guariglia et al., 1993). Sometimes, patients will transfer details from the left to the right-
hand side, as seen in Figure 6.49. This is called allesthesia or allochiria (Meador et al., 1991). The examples shown in Figure 6.51 illustrate the profound consequences that brain damage can have on perceptual behaviour, not just in terms of behavioural impairment but also in terms of disruption to a patient’s life and work. The reasons for spatial neglect are unclear (see Halligan and Marshall, 1994, and Mozer et al., 1997, for a discussion).
Psychology in action – How does brain injury affect artists? Losing the ability to speak, to recall information, or organise and plan everyday life efficiently are all unwelcome intruders in the world of the normally functioning. But what if the disrupted function is essential to the person’s life and provides him or her with a livelihood? Beethoven composed symphonies, Evelyn Glennie plays exceptional xylophone, Stevie Wonder is an accomplished keyboardist; even James Joyce managed to produce Ulysees and Finnegan’s Wake despite his chronic sight loss (although this is thought to explain some of Joyce’s eccentric text). None of these, however, despite their sensory losses, sustained brain injury. Chatterjee (2004) has reviewed the type of effects brain injury has on an artist’s performance and output. The loss of the ability to perceive colour is clearly one of the most challenging problems for an artist who exploits his or her chromatic palette. Sacks (1995) describes an artist who developed an injury leaving him achromatopsic – the artist’s world appeared ‘dirty grey’ and he reported being unable to imagine colours (or even being able to dream in colour). Before the accident leading to the injury, the patient painted colourful, abstract creations; after the accident, the paintings became figurative and abstract. Contrast, figure and form were
good as was the patient’s ability to understand and describe colour but his use of colour became haphazard. Unilateral spatial neglect has more intriguing, if predictable, consequences. Jung (1974) described four early cases of painters who developed neglect following brain injury. One, the German artist Lovis Corinth, had suffered a right hemisphere stroke. His painting changed dramatically: the contours on the left of his work disappeared and details became misplaced. Blanke et al. (2003) reported the case of a 71-year-old artist who could colour the right side of her paintings normally and evenly but paid minimal attention to the left. Figure 6.50 gives an example of the patient’s art following injury. Neglect for colour was greater than neglect for form in the majority of the patient’s paintings. Painter IK showed right neglect where entire canvasses would be created in exuberant colour but the right side lacked detail and form (Marsh and Philwin, 1987). Perhaps the most famous example of unilateral spatial neglect is the Italian film director, Federico Fellini, whose disorder was reported by Cantagallo and Della Sala (1998). At the age of 73, Fellini suffered a stroke in the middle cerebral artery of the right parietal lobe that caused left extrapersonal spatial
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Psychology in action – Continued (a)
(b)
Figure 6.50 The colour neglect seen in a drawing by Blanke et al.’s patient. Source: Plate 6.2 from Human Neuropsychology, 2nd edn, Pearson/Prentice Hall (Martin, G.N., 2006). Image kindly provided by Dr Olaf Blanke.
Figure 6.51 Italian film director Federico Fellini developed spatial neglect after suffering a stroke. As well as being a director, Fellini was also a talented cartoonist and he doodled comically on his psychological tests. (a) and (b) Examples of Fellini’s spatial neglect test performance. Source: Chatterjee, A. A madness to the methods of cognitive neuroscience? Journal of Cognitive Neuroscience, 2005, 17, 6, 847–9, © by the Massachusetts Institute of Technology.
At least neglect patients can recognise their creations. Some patients with visual agnosia are unable to do this. Wapner et al. (1978) report the case of a 73-year-old amateur artist who developed visual agnosia following a stroke. The artist would draw extremely laboriously but failed to recognise what he drew. He could identify the general shape of the object and describe its function, and even tried to identify it from its parts, but could not put a label to it. His agnosia was perceptual, rather than conceptual, because he would sometimes describe the functions of parts of the object he drew (e.g. what a telephone was for).
M
neglect that persisted for two months. As well as being a celebrated film director, Fellini was an accomplished cartoonist and his completion of neglect tests was peppered with his cartoonish embellishments. His original cartoons showed neglect of the left side. Figure 6.51 (a) and (b) illustrates some of Fellini’s attempts. Fellini’s neglect did not appear to be representational (he could imagine both sides of his visual field) and he was completely aware of his deficits. Unlike patients in previous reports, his increased awareness did not lead to a decrease in his neglect (Guariglia et al., 1993). Halligan and Marshall (1997) reported the consequences of neglect for a 75-year-old artist and sculptor who had suffered a right hemisphere stroke. Six months after the stroke, his drawings were poorer and less elaborate than they were before the stroke. His family also noted that he seemed to concentrate on the right-hand side of the drawings. In fact, on all the standard tests of neglect, he showed impairment. Figure 6.52 (a)–(c) shows examples of the patient’s sculptures before and 3 to 4 months after the stroke. As Fellini did, some artists can recover their ability to attend to the left to some extent; sometimes they will use broader strokes than normal or may be more expressive, as the painters Loring Hughes and Lovis Corinth found.
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Psychology in action – Continued con-
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Figure 6.52 These show the effects of brain damage on the work of a sculptor. (a) A sculpture made before the injury. (b) Another sculpture made after the injury. (c) A drawing made by the same artist after injury. Source: Halligan, P. and Marshall, J., The art of visual neglect, The Lancet, 1997, 350, July, pp. 139–140. © 1997 The Lancet Limited.
Agnosic patients can sometimes imagine the objects they would like to draw. Botez et al. (1985), however, report the case of a 38-year-old teacher and amateur charcoal drawer who was unable to imagine people, places or objects, following dilation of one of the brain’s chambers. Copying objects presented little problem but when the object was removed from sight, her drawings became simple and schematic. When she was given the name of an object to draw, she could not do this competently. Perception seems the most likely casualty in the artist’s battle with brain damage but there are some cases of impairment to other functions which lead to some unusual artistic
sequences. The Bulgarian artist Zlatio Boiyadjiev, exhibited a natural, pictorial style prior to the development of aphasia (Zaimov et al., 1969). After the aphasia, his art became bold, rich and colourful, full of striking, energetic lines and replete with bizarre imagery. Another artist with aphasia, the Polish artist RL (an Assistant Professor in Lublin), was known for highly symbolic paintings. Following aphasia, he produced very well-executed charcoal drawings, self-portraits and landscapes (Kaczmarek, 1991). No matter how hard he tried, he never did recover the symbolism of his art that existed before the aphasia.
Chapter review Perception of form • Perception of form requires recognition of figure and ground. The Gestalt organisational laws of proximity, similarity, good continuation and common fate describe some of the ways in which we distinguish figure from ground even when the outlines of the figures are not explicitly bounded by lines. • One hypothesis concerning the mechanism of pattern perception, or visual recognition of particular shapes suggests that our brain contains templates of all the shapes we can perceive. We compare a particular pattern of visual input with these templates until we find a fit. A second hypothesis suggests that our brain contains prototypes, which are more flexible than simple templates. Some psychologists believe that prototypes
are collections of distinctive features (such as the two parallel lines and the connecting diagonal of the letter N). • Perception involves both bottom-up and top-down processing. Our perceptions are influenced not only by the details of the particular stimuli we see, but also by their relations to each other and our expectations. Thus, we may perceive a shape either as a loaf of bread in the kitchen or as a letterbox alongside a country road, for example. • We can usually distinguish male and female faces on the basis of eyes, mouth and nose but rarely on the basis of single features alone. • Lighting, form and contour significantly influence our ability to recognise faces correctly.
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SUGGESTIONS FOR FURTHER READING
reappearance somewhere else as movement of that object. Because of the phi phenomenon, we perceive television shows and films as representations of reality, not as a series of disconnected images.
Perception of space and motion • Because the size and shape of a retinal image vary with the
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location of an object relative to the eye, accurate form perception requires depth perception – perception of the locations of objects in space. Depth perception comes from binocular cues (from convergence and retinal disparity) and monocular cues (from interposition, size, linear perspective, texture, haze shading, elevation, and the effects of head and body movements). The Sapir–Whorf hypothesis suggests that language can strongly affect the way we perceive the world although there is not much research to support it. It is possible that experience with some environmental features, such as particular geographical features or buildings composed of straight lines and right angles, has some influence on the way people perceive the world. We perceive the brightness of an object relative to that of objects around it; thus, objects retain a constant brightness under a variety of conditions of illumination. In addition, our perception of the relative distance of objects helps us maintain form constancy. Because our bodies may well be moving while we are visually following some activity in the outside world, the visual system has to make further compensations. It keeps track of the commands to the eye muscles and compensates for the direction in which the eyes are pointing. Movement is perceived when objects move relative to one another. In particular, a smaller object is likely to be perceived as moving across a larger one. Movement is also perceived when our eyes follow a moving object, even though its image remains on the same part of the retina and supplies important cues about an object’s three-dimensional shape. Because a complex scene, covering a large area, cannot be seen in a single glance, the visual system must combine information from successive fixations. The phenomenon of backward masking suggests that the image received from the previous fixation is erased immediately after a saccade so that blurring does not occur. The phi phenomenon describes our tendency to see an instantaneous disappearance of an object and its
Brain mechanisms of visual perception • Visual information proceeds from the retina to the thalamus,
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and then to the primary visual cortex (PVC). The PVC is organised into modules, each of which receives information from a small region of the retina. Neural circuits within each module analyse specific information from their part of the visual field, including the orientation and width of lines, colour and movement. The different types of information analysed by the neural circuits in the modules of the PVC are sent to separate maps of the visual field in the first level of the visual association cortex. The information from these maps is combined in the second level of the visual association cortex: form perception in the base of the temporal lobe and spatial perception in the parietal lobe. The brain seems to contain visual systems which process (1) features of objects and (2) the space indication of objects. The first, the ventral stream, projects from the PVC to the inferior temporal cortex; the second, the dorsal stream projects from the PVC to the posterior parietal cortex. Visual agnosia is the inability to perceive objects accurately (apperceptive agnosia) or assign meaning to visually presented objects (associative agnosia). Prosopagnosia is the inability to identify familiar faces and results from bilateral or unilateral posterior brain damage. The agnosic deficits seen in patient DF may be due to an intact dorsal stream but an impaired ventral stream. Blindsight refers to the ability to perform visual perceptual tasks despite a lack of awareness of the perceived stimuli; it is normally associated with damage outside the primary visual cortex. Spatial neglect is the inability to attend to stimuli in one half of space. Patients usually neglect the left-hand side as a result of right parietotemporal cortex damage (that is, the deficit is contralesional – occurs on the opposite side to the brain damage).
Suggestions for further reading Perception – general Coren, S., Ward, L.M. and Enns, J.T. (2003) Sensation and perception (6th edn). Chichester: Wiley. Goldstein, E.B. (2004) Blackwell Handbook of Sensation and Perception. Oxford: Blackwell. Levine, M.W. and Shefner, J.M. (2000) Fundamentals of Sensation and Perception. Oxford: Oxford University Press.
Ramachandran, V.S. and Rogers-Ramachandran, D. (2007) Paradoxical perceptions. Scientific American Mind, 18, 2, 18–20. Schiffman, H.R. (2000) Sensation and Perception: An integrated approach (5th edn). Chichester: Wiley. All of these books provide a good, solid description and evaluation of the topics covered in this (and the previous) chapter.
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Visual perception: general aspects Bruce, V., Green, P. and Georgeson, M. (2003) Visual Perception (4th edn). Hove: Psychology Press. Snowden, R., Thompson, P. and Troscianko, T. (2006) Basic Vision. Oxford: Oxford University Press. The Bruce et al. text gives a good introduction to the visual system, as does Snowden et al.
Visual recognition/awareness Chatterjee, A. (2004) Neuropsychology of art. Neuropsychologia, 42, 1568–83. Conway, B.R. and Livingstone, M.S. (2007) Perspectives on science and art. Current Opinion in Neurobiology, 17, 476–82. Cowey, A. (2004) The 30th Sir Frederick Bartlett lecture: fact, artefact, and myth about blindsight. The Quarterly Journal of Experimental Psychology, 57A, 4, 577–609. Goodale, M. and Milner, D. (2005) Sight Unseen: An exploration of conscious and unconscious vision. Oxford: Oxford University Press. Gruter, T. (2006) Picture this – how does the brain create images in our minds? Scientific American Mind, 17, 1, 18–23. This selection of very good readings covers various aspects of visual processing.
Farah, M.J. (2001) The Cognitive Neuroscience of Vision. Oxford: Oxford University Press. Gruter, T. (2007) Forgetting faces. Scientific American Mind, 18, 3, 68–73. Gruter, T., Gruter, M. and Carbon, C-C. (2008) Neural and genetic foundations of face recognition and prosopagnosia. Journal of Neuropsychology, 2, 79–97. Johnston, V.S. (2006) Mate choice decisions: The role of facial beauty. Trends in Cognitive Sciences, 10, 1, 10–13. Martin, G.N. (2006) Human Neuropsychology (2nd edn). Harlow: Prentice Hall Europe. Taylor, M.J., Batty, M. and Itier, R.J. (2004) The faces of development: A review of early face processing over childhood. Journal of Cognitive Neuroscience, 16, 8, 1426–42. Weiskrantz, L. (1997) Consciousness Lost and Found: A neuropsychological exploration. Oxford: Oxford University Press. Some useful and interesting specific and general reading on agnosia and face perception.
Spatial neglect Cantagallo, A. and Della Sala, S. (1998) Preserved insight in an artist with extrapersonal spatial neglect. Cortex, 34, 163–89. A good description of the consequences of brain damage on spatial neglect.
Visual agnosia and face perception Bruce, V. and Young, A.W. (1998) In the Eye of the Beholder: The science of face perception. Oxford: Oxford University Press.
Journals to consult Brain
Perception
British Journal of Psychology
Perception and Psychophysics
Cognitive Neuropsychology
Perceptual and Motor Skills
Cortex
Psychological Science
Journal of Experimental Psychology: Human perception and performance
Quarterly Journal of Experimental Psychology
Nature
Trends in Neuroscience
Neuropsychologia
Vision Research
Neuropsychology
Visual Neuroscience
Neuroscience
Trends in Cognitive Science
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WEBSITE ADDRESSES
Website addresses http://coglab.wadsworth.com/ This is a site that will allow you access to various experiments and demonstrations in experimental psychology. The site requires you to register before viewing the material. http://www.essex.ac.uk/psychology/interest.html You’ll find a collection of online experiments here on various aspects of visual perception. http://www.exploratorium.edu A collection of demonstrations of visual illusions from The Exploratorium.
http://cns-web.bu.edu/pub/laliden/WWW/Visionary/Visionary.html An online dictionary of terms used in visual perception. http://www.yorku.ca/eye An online textbook called The Joy of Visual Perception, written by Peter Kaiser at York University. http://www.faceresearch.org/exp An excellent site featuring experiments on face perception run by the University of Aberdeen.
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Learning and behaviour
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Luck can change your life Ms V is a compulsive gambler. It wrecked her marriage and drained her wallet long ago. Her kids don’t like her because she is always barely scraping by – and borrowing money from them – waiting for the next big win that she hopes will give her all the cash she needs to escape her current mess. How did it all begin? The answer lies in the schedules of reinforcement. At college, one of her boyfriends liked to bet on the horses and V went along one day. She bet £10 on a filly named Flo and won £300. What a rush! Luck brought her a giant reinforcer without much effort – with no ‘down side’ in sight. Her boyfriend was excited, too. V saved the money and went back to the track several more times over the next several weeks – sometimes alone, sometimes with her boyfriend – making more £10 bets. Most lost. A few made small wins. But the betting was exciting, and there was lots of sensory stimulation when her horse took one of the front positions. When V’s £300 was about half gone, she bet on a long shot with big odds. No one expected Viceroy to win, but V put down £75 on a hunch. Viceroy. . . won by a nose. V walked away with £4,500 in her pocket. Early periods of generous reinforcement can have a big effect on our later behavioural decisions. Source: adapted Baldwin and Baldwin (1998)
WHAT YOU SHOULD BE ABLE TO DO AFTER READING CHAPTER 7
• Describe the concept of habituation and the phenomena of classical conditioning and operant learning.
• Understand the principles underlying classical conditioning.
• Understand the principles underlying operant conditioning.
• Describe and explain conditioned aversions. • Describe the nature of insight. • Apply the principles of learning theory to behaviour. • Describe some of the factors that influence academic learning.
QUESTIONS TO THINK ABOUT
• Do different aspects of learning have different underlying principles? Is learning to ride a bike governed by different principles from those used for learning to find your way around college or university or learning a foreign language?
• Does all learning have to be intentional? Can you learn something without knowing it or without wanting to learn it?
• What factors do you think enhance and promote the process of learning?
• What psychological factors can enhance (or impair) your academic learning?
• In what way is the brain like a computer (and vice versa)?
• Is learning a process that depends on innate ability, the ability to adopt successful learning strategies or both? Explore the accompanying video, simulations, and animations on MyPsychLab. This chapter includes activities on: Acquisition of conditioned responses • Stimulus generalisation and stimulus discrimination • Classical conditioning of Little Albert • Schedules of reinforcement • Check your understanding and prepare for your exams using the multiple choice, short answer and essay practice tests also available
CHAPTER 7
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The purpose of learning Behaviours that produce favourable consequences are repeated and become habits, but those that produce unfavourable consequences tend not to recur (Ouellette and Wood, 1998). In other words, we learn from experience. Learning is an adaptive process in which the tendency to perform a particular behaviour is changed by experience. As conditions change, we learn new behaviours and eliminate old ones. This chapter considers three kinds of learning: habituation, classical conditioning and operant conditioning. All three involve cause-and-effect relations between behaviour and the environment. We learn which stimuli are trivial and which are important, and we learn to make adaptive responses and to avoid maladaptive ones. We learn to recognise those conditions under which a particular response is useful and those under which a different response is more appropriate. The types of learning described in this chapter serve as the building blocks for more complex behaviours, such as problem-solving and thinking, which we consider in later chapters. Learning, however, cannot be truly observed in a direct sense; it can only be inferred from changes in behaviour. As you saw in Chapter 1, the influential field of behaviourism which dominated experimental psychology in the early twentieth century demanded that only observable behaviour could be valid subject matter for psychologists. However, even the founding father of behaviourism, John B. Watson, argued that there could be two categories of observable behaviour: explicit behaviour, which is directly observable to the eye, and implicit behaviour, which could be measured by special equipment (an example would be the measurement of bodily response using psychophysiological recording equipment). But not all changes in behaviour are caused by learning. For example, your performance in an examination or the skill with which you operate a car can be affected by your physical or mental condition, such as fatigue, fearfulness or distraction. Moreover, learning may occur without noticeable changes in observable behaviour taking place. In some cases, learning is not apparent – at least, not right away – from our observable behaviour. In other cases, we may never have the opportunity to demonstrate what we have learned. For example, although you may have received training in how to conduct an orthogonally rotated factor analysis in your computer’s statistics package, you may never need to demonstrate the results of your learning again. In still other cases, you may not be sufficiently motivated to demonstrate something you have learned. For example, a tutor might pose a question in a seminar but although
you know the answer, you do not say anything because you get nervous when speaking in front of others. Learning takes place within the nervous system. Experience alters the structure and chemistry of the brain, and these changes affect the individual’s subsequent behaviour. Performance is the behavioural change (or new behaviour) produced by this internal change.
Habituation Many events may cause us to react automatically. For example, a sudden, unexpected noise causes an orienting response: we become alert and turn our heads towards the source of the sound. However, if the noise occurs repeatedly, we gradually cease to respond to it; we eventually ignore it. Habituation, learning not to respond to an unimportant event that occurs repeatedly, is the simplest form of learning. As you will see in Chapter 12, even infants a few months old show evidence of habituation. From an evolutionary perspective, habituation makes adaptive sense. If a once-novel stimulus occurs again and again without any important result, the stimulus has no significance to the organism. Obviously, responding to a stimulus of no importance wastes time and energy. The simplest form of habituation is temporary, and is known as short-term habituation. Imagine entering a new room in an inhabited house. It is likely that you will perceive the distinctive odour of the room. Eventually, however, you begin not to notice the odour; you will have become habituated. If you return to the same house the next day, however, you will perceive that distinctive smell again but if you stay in the room for long enough, you will again become habituated.
Classical conditioning Unlike habituation, classical conditioning involves learning about the conditions that predict that a significant event will occur. We acquire much of our behaviour through classical conditioning. For example, if you are hungry and smell a favourite food cooking, your mouth is likely to water. If you see someone with whom you have recently had a serious argument, you are likely to experience again some of the emotional reactions that occurred during the encounter. If you hear a song that you used to listen to with a loved one, you are likely to experience a feeling of nostalgia. If you listen to a piece of music that can be distinctly identified by nation, then people will buy more of that nation’s wine. How does such classical conditioning take place?
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Imagine that you have an uninflated balloon directly before you. Someone starts inflating the balloon with a pump; the balloon gets larger and larger. What are you likely to do? You will probably grimace and squint your eyes as you realise that the balloon is about to burst in your face. Now consider how a person learns to flinch defensively at the sight of a tightly stretched balloon. Suppose that we inflate a balloon in front of a young boy who has never seen one before. The boy will turn his eyes towards the enlarging balloon, but he will not flinch. When the balloon explodes, the noise and the blast of air will cause a defensive startle reaction: he will squint, grimace, raise his shoulders and suddenly move his arms towards his body. A bursting balloon is an important stimulus, one that causes an automatic, unlearned defensive reaction. We will probably not have to repeat the experience many times for the boy to learn to react the way we all do – flinching defensively before the balloon actually bursts. A previously neutral stimulus (the over-inflated balloon), followed by an important stimulus (the explosion that occurs when the balloon bursts), can now trigger the defensive flinching response by itself. The defensive flinching response has been classically conditioned to the sight of an over-inflated balloon. Two stimuli have become associated with each other.
Pavlov’s serendipitous discovery In December 1904, the Russian physiologist Ivan Pavlov was awarded the Nobel Prize in physiology and medicine for his work on the digestive system. Invited to Stockholm to accept the award and to deliver an acceptance speech, the 55-year-old Pavlov did not speak of his pioneering work on digestion (Babkin, 1949). Instead, his address, entitled ‘The first sure steps along the path of a new investigation’, focused on his more recent work involving conditional reflexes or ‘involuntary’ responses. Pavlov’s new line of research was to take him far from the research for which he was awarded the Nobel Prize, and today he is remembered more for his work in psychology than in physiology. But it was while studying the digestive system that Pavlov stumbled on the phenomenon that was to make a lasting impact on psychology (Windholz, 1997). Pavlov’s chief ambition as a physiologist was to discover the neural mechanisms controlling glandular secretions during digestion. He measured the secretions during the course of a meal by inserting a small tube in a duct in an animal’s mouth and collecting drops of saliva as they were secreted by the salivary gland. During each of the test sessions, he placed dry food powder inside the dog’s mouth and then collected the saliva. All went well until the dogs became experienced subjects. After several
testing sessions, the dogs began salivating before being fed, usually as soon as they saw the laboratory assistant enter the room with the food powder. What Pavlov discovered was a form of learning in which one stimulus predicts the occurrence of another. In this case, the appearance of the laboratory assistant predicted the appearance of food. Rather than ignoring this phenomenon or treating it as a confounding variable that needed to be controlled, Pavlov designed experiments to discover exactly why the dogs were salivating before being given the opportunity to eat. He suspected that salivation might be triggered by stimuli that were initially unrelated to eating. Somehow, these neutral stimuli came to control what is normally a natural reflexive behaviour. After all, dogs do not naturally salivate when they see laboratory assistants. To do so, he placed an inexperienced dog in a harness and occasionally gave it small amounts of food powder. Before placing the food powder in the dog’s mouth, Pavlov sounded a bell, a buzzer or some other auditory stimulus. At first, the dog showed only a startle response to the sound, perking its ears and turning its head towards the sound. The dog salivated only when the food powder was placed in its mouth. But after only a dozen or so pairings of the bell and food powder, the dog began to salivate when the bell rang. Placing the food powder in the dog’s mouth was no longer necessary to elicit salivation; the sound by itself was sufficient. Pavlov showed that a neutral stimulus can elicit a response similar to the original reflex when the stimulus predicts the occurrence of a significant stimulus (in this case, food powder). This type of learning is called classical or Pavlovian conditioning. Pavlov demonstrated that conditioning occurred only when the food powder followed the bell within a short time. If there was a long delay between the sound and the food powder or if the sound followed the food powder, the animal never learned to salivate when it heard the sound. Thus, the sequence and timing of events are important factors in classical conditioning. Classical conditioning provides us with a way to learn cause-and-effect relations between environmental events. We are able to learn about the stimuli that warn us that an important event is about to occur. Obviously, warning stimuli must occur prior to the event about which we are being warned. Figure 7.1 shows the basic classical conditioning procedure – the special conditions that must exist for an organism to respond to a previously neutral stimulus. A stimulus, such as food, that naturally elicits reflexive behaviour, such as salivation, is called an unconditional stimulus (UCS). The reflexive behaviour itself is called the unconditional response (UCR). If, for a certain dog, a bell signals food, then the bell may also come to elicit salivation through classical conditioning. Another dog may hear the sound of an electric can opener just before it is
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Figure 7.1 Basic components of the classical conditioning procedure. Prior to conditioning, the UCS but not the CS elicits a response (the UCR). During conditioning, the CS is presented in conjunction with the UCS. Once the conditioning is completed, the CS alone elicits a response (the CR).
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Salivation is an innate behaviour and is adaptive because it facilitates digestion. Through natural selection, the neural circuitry that underlies salivation has become part of the genetic endowment of many species. Pavlov’s experiments demonstrated that an innate reflexive behaviour, such as salivation, can be elicited by novel stimuli. Thus, a response that is naturally under the control of appropriate environmental stimuli, such as salivation caused by the presence of food in the mouth, can also come to be controlled by other kinds of stimulus. Classical conditioning accomplishes two functions. First, the ability to learn to recognise stimuli that predict the occurrence of an important event allows the learner to make the appropriate response faster and perhaps more effectively. For example, hearing the buzz of a wasp near your head may make you duck and avoid being stung. Seeing a rival increases an animal’s heart rate and the flow of blood to its muscles, makes it assume a threatening posture, and causes the release of hormones that prepare it for vigorous exercise. The second function of classical conditioning is even more significant. Through classical conditioning, stimuli that were previously unimportant acquire some of the
Basic principles of classical conditioning
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properties of the important stimuli with which they have been associated and thus become able to modify behaviour. A neutral stimulus becomes desirable when it is associated with a desirable stimulus or it becomes undesirable when it is associated with an undesirable one. In a sense, the stimulus takes on symbolic value. For example, we respond differently to the sight of a stack of money and to a stack of paper napkins. The reason for the special reaction to money is that money has, in the past, been associated with desirable commodities, such as food, clothing, cars, electrical equipment and so on.
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fed, in which case that sound will come to elicit salivation. A neutral stimulus paired with the unconditional stimulus that eventually elicits a response is called a conditional stimulus (CS). The behaviour elicited by a conditional stimulus is called a conditional response (CR). In the case of Pavlov’s dogs, food powder was the UCS: it elicited the UCR, salivation. At first, when Pavlov presented the sound of the bell or buzzer, the dogs did not salivate; the sound was merely a neutral stimulus, not a CS. However, with repeated pairings of the sound and the food powder, the sound became a CS, reliably eliciting the CR – salivation.
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Classical conditioning involves several learning principles, including acquisition, extinction, spontaneous recovery, stimulus generalisation and discrimination.
Acquisition In laboratory experiments, a single pairing of the CS with the UCS is not usually sufficient for learning to take place. Only with repeated CS–UCS pairings does conditional responding gradually appear. The learning phase of classical conditioning, during which the CS gradually increases in frequency or strength, is called acquisition. In one study (Trapold and Spence, 1960), a tone (CS) was paired with a puff of air into the eye (UCS). The puff of air caused the participants’ eyes to blink automatically (UCR). Conditioning was measured as the percentage of trials in which conditional eyeblinks (CR) occurred. Note that at the beginning of the experiment, the tone elicited very few CRs. During the first 50 trials, the percentage of CRs increased rapidly but finally stabilised. Two factors that influence the strength of the CR are the intensity of the UCS and the timing of the CS and UCS. The intensity of the UCS can determine how quickly the CR will be acquired: more intense UCSs usu-
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e No two stimuli are exactly alike. Once a response has been conditioned to a CS, simiyp sych lar stimuli will also elicit that response. The more closely the other stimuli resemble the CS, the more likely they will elicit the CR. For example, Pavlov discovered that once a dog learned to salivate when it heard a bell, it would salivate when it heard a bell having a different tone or when it heard a buzzer. This phenomenon is called generalisation: a response produced by a particular CS will also occur when a similar CS is presented. Of course, there are limits to generalisation. A dog that learns to salivate when it hears a bell will probably not salivate when it hears a door close in the hallway. In addition, an organism can be taught to distinguish between similar but different stimuli – a phenomenon called discrimination. Discrimination training is accomplished by using two different CSs during training. One CS is always followed by the UCS; the other CS is never followed by the UCS. For example, suppose that we regularly direct a puff of air at an animal’s eye during each trial in which a low-pitched tone (CS+) is sounded, but on trials in which a high-pitched tone (CS−) is sounded, we present no air puff. At first, increased amounts of blinking will occur in response to both stimuli (generalisation). Gradually, however, fewer and fewer blinks will occur after the CS– but they will continue to be elicited by the CS+ (see Figure 7.3). Discrimination, then, involves learning the difference between two or more stimuli. An animal learns that differences among stimuli are important – it learns when to respond to one stimulus and when not to respond to a different stimulus.
Conditional emotional responses UCS Time
Figure 7.2 The timing of the CS and UCS in classical conditioning. The CS precedes the UCS by a brief interval of time, and both stimuli end simultaneously.
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Once a classically conditioned response has been acquired, what happens to that response if the CS continues to be presented but is no longer yp sych followed by the UCS? This procedure, called extinction, eventually eliminates the CR. Returning to our classically conditioned eyeblink response, suppose that after we reduce the intensity of the UCS, we stop presenting the UCS (the puff of air). However, we do continue to present the CS (the tone). It is important to realise that extinction occurs only when the CS occurs but the UCS does not. For example, the eyeblink response will extinguish only if the tone is presented without the puff of air. If neither stimulus is presented, extinction will not occur. In other words, the subject must learn that the CS no longer predicts the occurrence of the UCS– and that cannot happen if neither stimulus is presented. ee
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Once a CR has been extinguished, it may not disappear from the organism’s behaviour permanently. Pavlov demonstrated that after responding had been extinguished, the CR would often suddenly reappear the next time the dog was placed in the experimental apparatus. Pavlov referred to the CR’s reappearance after a ‘time out’ period as spontaneous recovery. He also found that if he began presenting the CS and the UCS together again, the animals would acquire the conditional response very rapidly – much faster than they did in the first place.
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ally produce more rapid learning. For example, rats will learn a conditioned fear response faster if they receive higher levels of a painful stimulus (Annau and Kamin, 1961). Classical conditioning of a salivary response in dogs occurs faster when the animals are given larger amounts of food (Wagner et al., 1964). Generally speaking, the more intense the UCS, the stronger the CR. The second factor affecting the acquisition of the CR is the timing of the CS and UCS. Classical conditioning occurs fastest when the CS occurs shortly before the UCS and both stimuli end at the same time. In his experiments on salivary conditioning, Pavlov found that one halfsecond was the optimal delay between the onset of the CS and the onset of the UCS. With shorter or longer delays between the CS and UCS, conditioning generally was slower and weaker (see Figure 7.2).
Many stimuli are able to arouse emotional responses, such as feelings of disgust, contempt, fear, anger, sadness, tenderness, longing or sexual desire. Many of these stimuli, such as a place, a phrase, a song or someone’s voice and face, originally had no special significance. But because these stimuli were paired with other stimuli that
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Figure 7.3 Behaviour produced through discrimination training. The CS+ is always followed by the UCS (a puff of air directed towards the eye); the CS– is always presented without the UCS.
elicited strong emotional reactions, they came, through classical conditioning, to take on emotional significance. If you read or hear words such as ‘enemy’, ‘ugly’, ‘bitter’ or ‘failure’, you are likely to experience at least a weak negative emotional response. In contrast, the words ‘gift’, ‘win’, ‘happy’ and ‘beauty’ may elicit positive responses. These words had no effect on you before you learned what they meant. They took on their power through being paired with pleasant or unpleasant events or perhaps with descriptions of such events. Staats and Staats (1957) found that if people read neutral nonsense words such as ‘yof’ or ‘laj’ while hearing positive or negative words, they later said that they liked those that had been associated with the positive words and disliked those that had been associated with the negative ones. The researchers found that this procedure could even affect people’s ratings of the pleasantness of names such as Tom or Bill or nationalities such as Italian or Swedish (Staats and Staats, 1958). Berkowitz (1964) found that when people had received unpleasant electrical shocks while in the company of another person, they later acted in a hostile manner towards that person. Thus, classical conditioning may play a role in the development of ethnic prejudices and personal dislikes (and, of course, of positive reactions as well). We are often not aware of the reason for our emotional reactions, we simply feel them and conclude that there is something ‘nice’ or something ‘nasty’ about the stimulus (or the person).
Phobias Many people are troubled by behaviours that they wish they could stop or by thoughts and fears that bother them. Phobias are unreasonable fears of specific objects or situations, such as spiders, cars or enclosed spaces, and we will look at phobias in more detail in Chapter 18.
Presumably, at some time early in life, the person having the phobia was exposed to the now-feared object in conjunction with a stimulus that elicited pain or fear. For example, being stuck in a hot, overcrowded lift with a group of frightened and sweating fellow passengers might be expected to lead to a fear of lifts or perhaps even to produce a fully-fledged phobia. Classical conditioning can occur even without direct experience with the conditional and unconditional stimuli. For example, a child of a parent who has a snake phobia can develop the same fear simply by observing signs of fear in his or her parent. The child need not be attacked or menaced by a snake. In addition, people can develop phobias vicariously – by hearing about or reading stories that vividly describe unpleasant episodes. The imaginary episode that we picture as we hear or read a story (UCS) can provide imaginary stimuli (CSs) that lead to real conditional emotional responses (CRs).
The case of Little Albert A famous example of an experimentally induced learned phobia is that of Little Albert. In Chapter 1 you came across the work and ideas of John B. Watson. To Watson, behaviour had to be observable in order to be measured. He was excited by Pavlov’s finding that dogs could be conditioned to respond in a specific way to a previously neutral stimulus. He and Rosalie Rayner set up the first experiment in which fear was experimentally conditioned in a human being (Watson and Rayner, 1920). At the age of nine months, a healthy infant called Albert B was shown to have no fear of live animals such as rats and rabbits (Albert is for ever known in textbooks as Little Albert). When a steel bar was unexpectedly struck by a claw hammer, however, he became distressed and frightened. Watson and Rayner attempted to condition fear of a previously unfeared object (a white rat) in Little Albert by pairing it with a feared stimulus (the noise of the hammer hitting the bar). They paired the rat with the noise seven times in two sessions, one week apart. When the rat was presented on its own, Albert became distressed and avoided the rat. Five days later, Albert was exposed to a number of other objects such as familiar wooden blocks, a rabbit, a dog, a sealskin coat, white cotton, the heads of Watson and two assistants and a Santa Claus mask. Albert showed a fear response to the rabbit, the dog and the sealskin coat. The initial conditioned response had generalised to some objects but not others. Watson and Rayner’s experiment is famous for two reasons. The first is the successful attempt at experimentally conditioning fear in a human being; the second is the number of inaccuracies reported in articles and textbooks
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describing the experiment (Harris, 1979). These include inaccurate information about Albert’s age, the conditioned stimulus and the list of objects that Albert was believed to be frightened of after conditioning (the list includes fur pelt, a man’s beard, a cat, a puppy, a glove, Albert’s aunt and a teddy bear). These inaccuracies teach a valuable lesson, and that is the wisdom of consulting original sources of information. Because the study of Albert is part of psychology’s history, details become distorted when information is passed down from textbook to textbook, a form of memory distortion described in more detail in the next chapter.
What is learned in classical conditioning? Research shows that for classical conditioning to occur, the CS must be a reliable predictor of the UCS (Rescorla, 1991). Imagine yourself as the subject in a classical conditioning demonstration involving a tone as the CS, a puff of air into your left eye as the UCS and an eyeblink as the CR. Your psychology lecturer asks you to come to the front of the class and seats you in a comfortable chair. Occasionally, a tone sounds for a second or two, and then a brief but strong puff of air hits your eye. The puff of air makes you blink. Soon you begin to blink during the tone, before the puff occurs. Now consider all the other stimuli in the seminar room – your tutor explaining the demonstration to the group, your colleagues’ questions, squeaks from students moving in their chairs, and so on. Why don’t any of these sounds become CSs? Why do you blink only during the tone? After all, some of these stimuli occur at the same time as the puff of air. The answer is that among the stimuli present during the demonstration, only the tone reliably predicts the puff of air. All the other stimuli are poor forecasters of the UCS. The neutral stimulus becomes a CS only when the following conditions are satisfied:
1 The CS must regularly occur prior to the presentation of the UCS. 2 The CS does not regularly occur when the UCS is absent. Consider another example. The smell of food is more likely to elicit feelings of anticipation and excitement about supper if you are hungry than is the smell of your mother’s cologne because the smell of the food is the best predictor of a meal about to be served. Similarly, the sound of footsteps behind you as you are walking is more apt to make you afraid than the sound of a car passing by or the wind blowing in the trees because the footsteps are better predictors of being mugged or threatened with danger. It also appears that conditioned responses are more common to novel than familiar stimuli. Pavlov had observed that a novel CS was more successfully paired with a UCS than was a familiar one. This phenomenon is
known as latent inhibition (Lubow, 1989), and because familiar stimuli are associated less successfully with conditioning than are novel ones, this effect is called the CS pre-exposure effect (because participants will have already been pre-exposed to the CS). Similarly, when an organism is presented with the UCS (which may be novel) before it is used as a UCS in the experiment proper, the link between CS and UCS is weaker. This is called the UCS pre-exposure effect (Randich and LoLordo, 1979). Why does latent inhibition occur? No one quite knows for sure, but one explanation is related to the degree of exposure to the stimulus. A familiar CS is familiar to individuals by being in the environment; because the CS is part of the environment of context then the CS becomes merged into the context of the conditioning. To use a description from signal detection theory which you learned about in Chapter 5, the signal-to-noise ratio is weak – the CS sends a weak signal because it cannot be distinguished from the context very well.
Neurobiological correlates of Pavlovian conditioning In an experiment to determine the brain regions involved in Pavlovian fear conditioning, participants were exposed to lights that signalled the appearance of a painful electric shock (conditioned stimulus, CS) or ones that did not (Knight et al., 1999). Functional magnetic resonance imaging (fMRI) was used to monitor differences in brain activation. As training and learning progressed, the amount of neuronal activity seen during the warning CS increased in a part of the brain called the anterior cingulate, in the front of the brain. When the light and shock were not paired (i.e. they were not associated), this activation did not occur. Although the researchers suggest that this part of the brain may not be neccessary for learning fear, it does facilitate the learning of fear. Another crucial structure for fear conditioning is the amygdala, and you will discover more about its role in fear recognition and conditioning in Chapter 13.
After behaviourism Pavlov’s work greatly influenced his colleagues abroad, especially the pioneers of behaviourist thinking such as John B. Watson. Behaviourism was a robust and experimentally strict discipline whose principles were laid out by Watson in the first and second decades of the twentieth century. It viewed behaviour and learning in terms of stimulus and response and, as the next evolution of behaviourism described in the next section shows, rein-
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forcement. The inner mind or introspective self-reports played no part in behaviourist thinking: these were unverifiable and held the same status as superstition to the behaviourist. Both stimulus and response could be observed and the effect of one on the other recorded. Behaviourism left a unique and historical legacy that is seen in almost all experimental work undertaken in psychology today; its effects were such that modern psychology has absorbed its principles and aims. The torch-bearers of behaviourism, however, began to modify elements of its thinking in the mid-twentieth century and although the effects of these modifications made no significant or lasting impact on psychology by themselves, the attempts at modification did because other, more dominant approaches to studying behaviour arose from them. Two influential psychologists, whose specific work did not have a long-lasting effect on the way psychology is studied, but did bequeath a way of thinking about learning and behaviour, were Clark L. Hull (1884– 1952) and Edward Chase Tolman (1886–1959).
Independent variables Deprivation of food, water, sex, etc.
Intervening variables
Dependent variables
D
Amplitude
Painful stimulation Magnitude of reward
K
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= = = =
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drive incentive motivation habit strength excitatory potential
Figure 7.4 A simplified version of Hull’s system. Source: Adapted from Hill W.F., Learning: A survey of psychological interpretation, 7th edn. Published by Allyn & Bacon, Boston, MA. Copyright © 1997 by Pearson Education. By permission of the publisher.
Hull’s computational approach to learning Of all the learning theories reviewed in this chapter, Hull’s is probably the most ambitious and complicated of them. In his two published books, Principles of Behaviour (1943) and A Behaviour System (1952), Hull made extremely detailed predictions about behaviour that could occur in specific situations. The books contained 153 theorems that ranged from considering how we learn to discriminate, to moving in space, to how we acquire our values, and Hull’s aim was to develop a system whereby behaviour could be predicted from specified independent variables (IVs). You can quickly appreciate why the approach is seen as ambitious and complicated. Hull organised his system by considering what Watson’s behaviourism did not wish to: intervening variables, the variables that could modify the relationship between stimulus and response. In Hull’s system, analysis of behaviour comprised four stages: Stage 1 Analysis of the IVs from which behaviour was predicted. Stage 2 Computing values for intervening variables. Stage 3 Computing values at this stage, using values at stage 2. Stage 4 Analysis of the dependent variables (DVs). In summary, the stage process argued that knowing the values of an independent variable at stage 1 meant computing values of the intervening variables at stage 2, using these computed values to compute those at stage 3 and from this predict the outcome (or the dependent variable). Figure 7.4 summarises the main points of the system.
The number of independent variables were limitless and could range from direct stimulation (the brightness of light or the loudness of noise) to events that preceded the moment of study (such as degree of exercise taken or the amount of food consumed) to experiential episodes (such as the number of times a person had responded to the stimulus before). To produce a response (the DV), the IV would interact with the intervening variables at stages 3 and 4. These intervening variables were not directly observeable and were hypothetical states (you might see why Watson’s behaviourism would have rejected Hull’s approach). According to Hull, there were two types of intervening variable: habit strength and drive. You will find out more about these concepts and their validity in Chapter 13, but for now a simple definition of each would be: habit strength is the strength of the connections that had been learned between a stimulus and a response after reinforced practice had occurred; drive is a state of activation that propels an organism to seek stimulation (a reduction in the drive would serve as a reward). A drive represents a temporary state which is produced when the body has been deprived of something it needs, such as food, water, relief from pain, and so on. The greater the reward, therefore, the greater the reduction in drive: a slice of bread would not significantly reduce the drive for food, but a four course meal might. The greater the number of times a response was followed by reinforcement, the greater the formation of habit strength and the connections between a stimulus and its response. Hull also suggested another variable, incentive
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motivation, which would account for the organisms’s response to rewards of increasing size. As the above cursory description of the system suggests, Hull’s theory was complex and followed detailed mathematical formulae. His second book contained 133 theorems which, for good measure, followed on from 17 postulates and 15 corollaries. The apparent beauty and strength of Hull’s system was that one variable could be computed from another using these formulae. Where the system failed, however, was in using the values from a single experiment to predict later behaviour: this often did not work. Hull later stated that the values were meant to be regarded as illustrations rather than as fixed numbers and that, of course, values would vary across individuals. While Hull’s work has not had the direct influence and impact on later theory of some other schools of learning and behaviour, it represented an ambitious and laudable attempt at pinning down behaviour to values that could be computed and used to predict later behaviour.
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Like Hull, Tolman argued that there was more to the study of learning and behaviour than simply recording the stimulus and measuring the response. Tolman’s view was that a theory of behaviour should consider the cognitive variables that intercede between stimulus and response: our thoughts, beliefs, attitudes, motivation to succeed and so on are all important determinants of our response to a stimulus. Tolman’s approach was called purposive behaviourism and although, like the behaviourism it followed, it concerned itself with objective and observable behaviour and the external influences that could change it, it was also concerned with the cognitive processes that guided or gave rise to that behaviour. Behaviour had a purpose; it was executed to achieve a goal, hence, purposive behaviourism. According to Tolman, the behaviour that we engage in to achieve our goals is underpinned by our cognitions. Our cognitive processing can be measured by observing the way in which a person behaves or has experienced specific stimuli. For example, we might learn that chilli con carne tastes nicer with added ginger, cinnamon and three, rather than two, red chillies, so we make the chilli again adding these ingredients. None or any might make the chilli nicer but if none do, we experiment again either by adding or subtracting ingredients. Our experience – our cognitions – modifies our behaviour. Tolman’s most famous illustration of learning and the cognitions that lead to a response is that of reward loca-
tion. If an organism finds a way of locating a reward, it may eventually find a different, more efficient method, of locating it. If you imagine yourself in a strange town centre for the first time, your first successfully navigated route to a shop may be the longest, or least efficient one. With increasing knowledge of the environment, you will eventually find the shortest, quickest route to the shop you want. In Tolman’s experiment, rats were allowed to run on a table and through an enclosed alleyway which led to various elevated pathways at the end of one of which was some food (Tolman et al., 1946). When the rat had learned the location of the food, the alleyway was removed and replaced with new routes which went in different directions. Figure 7.5 shows you the difference between the two conditions. Tolman et al. found that, in the second condition, the rats did not take the route they had previously learned in order to obtain the food. Instead, they took a short-cut towards the direction of the food. According to Tolman, the rat had learned a ‘cognitive map’ of the routes and chose the shortest one. Although this seems eminently plausible, Tolman did not seem to consider that the rat may have taken the shortest route because the smell of the food led the rodent to it. This objection aside, Tolman’s influence was important because it rejected the stiff stimulus–response (S–R) approaches of behaviourism and encouraged an emphasis on the cognitive variables that shape behaviour. The essential principles of the approach can be seen in much
Goal D
E C
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Start B
Figure 7.5 The two pathways used in Tolman’s experiment. In the first, the rat takes the longer route in order to find the food. In the second, the original route is blocked and 18 new routes made available. The rats chose the tunnel marked C (that corresponding most closely to the location of the food), rather than D or E, the routes closest to that originally taken. Source: Hill W.F., Learning: A survey of psychological interpretation, 7th edn. Published by Allyn & Bacon, Boston, MA. Copyright © 1997 by Pearson Education. By permission of the publisher.
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Figure 7.6 A simulated view of a central corridor in a building used in Wilson et al.’s experiment. Source: Wilson, P. N., Foreman N. and Stanton, D. Improving spatial awareness in physically disabled children using virtual environments. Engineering Science and Education Journal, 1999, 8(5), 196–200, reprinted by permission of the Institute of Electrical Engineers.
of modern-day experiments on transfer of learning: the principle whereby learning in one environment can be successfully transferred to a different one. Work in virtual reality technology, for example, has been able to present participants with ‘virtual’ versions of environments which participants can navigate and explore before encountering the actual environment, thereby assisting navigation in the real version (Wilson et al., 1999). An example of one of these virtual images (part of an animated tour) can be seen in Figure 7.6. This image shows the ground floor central corridor of a simulated building (based on the psychology department at Leicester University, England). Wilson et al. (1996a) found that severely disabled children who explored this computer simulation were able to point successfully to objects in the real building when they later encountered it. A group of undergraduates who guessed the location of the objects, without having had the benefit of exposure to the computer simulation, performed less accurately. Tolman died just before the beginning of what is called in psychology, ‘the cognitive revolution’, which you read about in Chapter 1. However, his approach was a precursor to the cognitive revolution and prompted other disciplines, such as linguistics, to consider cognitive variables in their study. While Tolman’s ideas were superseded to some extent by developments in cognitive psychology, his work could be seen as the bedrock on which cognitive psychology’s general approach is based.
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The law of effect Operant conditioning was first discovered in the basement of a house in Cambridge, Massachusetts, by a 24-year-old man who would later become one of the twentieth century’s most influential educational psychologists, Edward L. Thorndike. Thorndike placed a hungry cat inside a ‘puzzle box’. The animal could escape and eat some food only after it operated a latch that opened the door. At first, the cat engaged in random behaviour: mewing, scratching, hissing, pacing and so on. Eventually, the cat would accidentally activate the latch and open the door. On successive trials, the animal’s behaviour would become more and more efficient until it was operating the latch without hesitation. Thorndike called this process ‘learning by trial and accidental success’. Thorndike explained that the cat learned to make the correct response because only the correct response was followed by a favourable outcome: escape from the box and the opportunity to eat some food. The occurrence of the favourable outcome strengthens the response that produced it. Thorndike called this relation between a response and its consequences the law of effect. The impact of Thorndike’s discovery of the law of effect on the early development of scientific psychology would be difficult to overstate. It affected research in the study of learning in one very important way: it stimulated an enormous number of experimental studies aimed at understanding behaviour–environment interactions, a line of research that is known today as behaviour analysis. Nowhere was this effect more evident than in the work of B.F. Skinner.
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Although Thorndike discovered the law of effect, Harvard psychologist Burrhus Frederic Skinner championed the laboratory study of the law of effect and advocated the application of behaviour analysis and its methods to solving human problems (Skinner, 1953, 1971; Mazur, 1994). He devised objective methods for studying behaviour, invented apparatus and methods for observing it, and created his own philosophy for interpreting it (Bolles, 1979). Moreover, he wrote several books for the general public, including a novel, Walden Two, that showed how his discoveries might be used for improving society (Skinner, 1948). One of Skinner’s most important inventions was the operant chamber (or Skinner box), an apparatus in which an animal’s behaviour can be easily observed, manipulated and automatically recorded (as seen in Figure 7.7). For example, an operant chamber used for rats is constructed so that a particular behaviour, such as pressing on a lever, will occasionally cause a pellet of food to be delivered. An operant chamber used for pigeons is built so that a peck at a plastic disc on the front wall will occasionally open a drawer that contains some grain. Behaviour analysts who study human behaviour use special devices suitable to the unique characteristics of their human subjects (Baron et al., 1991). In this case, instead of giving their participants some food, they give them points (as in a video game) or points exchangeable for money. Behaviour analysts manipulate environmental events to determine their effects on response rate, the number of responses emitted during a given amount of time. Events that increase response rate are said to strengthen responding; events that decrease response rate weaken b
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responding. To measure response rate, Skinner devised the cumulative recorder, a device that records each response as it occurs in time. The invention of the operant chamber and the cumulative recorder represent clear advances over Thorndike’s research methods because subjects can (1) emit responses more freely over a greater time period, and (2) be studied for longer periods of time without interference produced by the experimenter handling or otherwise interacting with them between trials. Under highly controlled conditions such as these, behaviour analysts have been able to discover a wide range of important behavioural principles.
The three-term contingency Behaviour does not occur in a vacuum. Sometimes a response will have certain consequences; sometimes it will not. Our daily behaviour is guided by many different kinds of discriminative stimuli – stimuli that indicate that behaviour will have certain consequences and thus sets the occasion for responding. For example, consider answering the telephone. The phone rings, you pick it up and say ‘hello’ into the receiver. Most of the time, someone on the other end of the line begins to speak. Have you ever picked up a telephone when it was not ringing and said, ‘hello’? Doing so would be absurd, because there would be no one on the other end of the line with whom to speak. We answer the phone (make a response) only when the phone rings (the preceding event) because, in the past, someone with whom we enjoy talking has been at the other end of the line (the following event). Skinner referred formally to the relationship among these three items – the preceding event, the response and the following event – as the three-term contingency (see Figure 7.8).
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Figure 7.7 An operant chamber. (This operant chamber is used for lever pressing by rats.)
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negative reinforcement, punishment, response cost and extinction. These consequences are always defined in terms of their effect on responding.
Discriminative stimulus
Positive reinforcement
sets the occasion for
A response
Strengthens connection between discriminative stimulus and response
sets the occasion for
Favourable consequences
Figure 7.8 The three-term contingency.
The preceding event – the discriminative stimulus – sets the occasion for responding because, in the past, when that stimulus occurred, the response was followed by certain consequences. If the phone rings, we are likely to answer it because we have learned that doing so has particular (and generally favourable) consequences. The response we make – in this case, picking up the phone when the phone rings and saying ‘hello’ – is called an operant behaviour. The following event – the voice on the other end of the line – is the consequence of the operant behaviour. Operant behaviour, therefore, occurs in the presence of discriminative stimuli and is followed by certain consequences. These consequences are contingent upon behaviour, that is, they are produced by that behaviour. In the presence of discriminative stimuli, a consequence will occur if and only if an operant behaviour occurs. In the absence of a discriminative stimulus, the operant behaviour will have no effect. Once an operant behaviour is established, it tends to persist whenever the discriminative stimulus occurs, even if other aspects of the environment change (Nevin, 1988; Mace et al., 1990). Of course, motivational factors can affect a response. For example, you might not bother to answer the telephone if you are doing something you do not want to interrupt.
Reinforcement, punishment and extinction Behaviour analysts study behaviour–environment interactions by manipulating the relations among components of the three-term contingency. Of the three elements, the consequence is the most frequently manipulated variable. In general, operant behaviours can be followed by five different kinds of consequence: positive reinforcement,
Positive reinforcement refers to an increase in the frequency of a response that is regularly and reliably followed by an appetitive stimulus. An appetitive stimulus is any stimulus that an organism seeks out. If an appetitive stimulus follows a response and increases the frequency of that response, we call it a positive reinforcer. For example, the opportunity to eat some food can reinforce a hungry pigeon’s pecking of a plastic disc. Money or other rewards (including social rewards) can reinforce a person’s behaviour. Suppose that you visit a new restaurant and really enjoy your meal. You are likely to visit the restaurant several more times because you like the food. This example illustrates positive reinforcement. Your enjoyment of the food (the appetitive stimulus) reinforces your going to the restaurant and ordering dinner (the response).
Negative reinforcement Negative reinforcement refers to an increase in the frequency of a response that is regularly and reliably followed by the termination of an aversive stimulus. An aversive stimulus is unpleasant or painful. If an aversive stimulus is terminated (ends or is turned off) as soon as a response occurs and thus increases the frequency of that response, we call it a negative reinforcer. For example, after you have walked barefoot across a stretch of hot pavement, the termination of the painful burning sensation negatively reinforces your response of sticking your feet into a puddle of cool water. It is important to remember that both positive and negative reinforcement increase the likelihood that a given response will occur again. However, positive reinforcement involves the occurrence of an appetitive stimulus, whereas negative reinforcement involves the termination of an aversive stimulus. Negative reinforcement is thus not the same as punishment.
Punishment Punishment refers to a decrease in the frequency of a response that is regularly and reliably followed by an aversive stimulus. If an aversive stimulus follows a response and decreases the frequency of that response, we call it a punisher. For example, receiving a painful bite would punish the response of sticking your finger into a parrot’s cage. People often attempt to punish the behaviour of their children or pets by scolding them.
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Although punishment is effective in reducing or suppressing undesirable behaviour in the short term, it can also produce several negative side effects: unrestrained use of physical force (for example, child abuse) may cause serious bodily injury. Punishment often induces fear, hostility and other undesirable emotions in people receiving punishment. It may result in retaliation against the punisher. Through punishment, organisms learn only which response not to make. Punishment does not teach the organism desirable responses. Reinforcement and punishment are most effective in maintaining or changing behaviour when a stimulus immediately follows the behaviour. It may occur to you that many organisms, particularly humans, can tolerate a long delay between their work and the reward that they receive for it. This ability appears to contradict the principle that reinforcement must occur immediately. However, the apparent contradiction can be explained by a phenomenon called conditioned reinforcement. Why is immediacy of reinforcement or punishment essential for learning? The answer is found by examining the function of operant conditioning: learning about the consequences of our own behaviour. Normally, causes and effects are closely related in time; you do something, and something immediately happens, good or bad. The consequences of our action teach us whether to repeat that action. Events that follow a response by a long delay were probably not caused by that response. It is important not to confuse punishment with negative reinforcement. Punishment causes a behaviour to decrease, whereas negative reinforcement causes a behaviour to increase.
of appetitive or aversive stimuli. Another way to change behaviour through operant conditioning is extinction, which involves no consequence at all. See Figure 7.9.
Extinction Extinction is a decrease in the frequency of a previously reinforced response because it is no longer followed by a reinforcer. Behaviour that is no longer reinforced decreases in frequency: it is said to extinguish. For example, a rat whose lever pressing was reinforced previously with food will eventually stop pressing the lever when food is no longer delivered. People soon learn to stop dropping money into vending machines that don’t work. A young boy will stop telling his favourite ‘knock-knock’ joke if no one laughs at it any more. Extinction is not the same as forgetting. Forgetting takes place when a behaviour is not rehearsed (or a person does not think about a particular memory) for a long time. Extinction takes place when an organism makes a response that is no longer reinforced. If the organism does not have an opportunity to make that response, it will not extinguish. For example, if you go out of town for a few weeks, you will not forget how to operate the vending
Reinforcement Appetitive stimulus Onset reinforces response Aversive stimulus
Negative reinforcement Termination reinforces response
Response cost Response cost refers to a decrease in the frequency of a response that is regularly and reliably followed by the termination of an appetitive stimulus. Response cost is a form of punishment. For example, suppose that you are enjoying a conversation with an attractive person that you have just met. You make a disparaging remark about a political party. Your new friend’s smile suddenly disappears. You quickly change the topic and never bring it up again. The behaviour (disparaging remark) is followed by the removal of an appetitive stimulus (your new friend’s smile). The removal of the smile punishes the disparaging remark. Response cost is often referred to as time-out from positive reinforcement (or simply time-out) when it is used to remove a person physically from an activity that is reinforcing to that person. As we have just seen, there are four types of operant conditioning – two kinds of reinforcement and two kinds of punishment – caused by the occurrence or termination
Positive reinforcement
Punishment Aversive stimulus
Punishment Onset punishes response
Appetitive stimulus
Response cost Termination punishes response Extinction
No stimulus
Extinction No contingency
Figure 7.9 Reinforcement, punishment and extinction produced by the onset, termination or omission of appetitive or aversive stimuli. The upward-pointing arrows indicate the occurrence of a response.
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Intermittent reinforcement
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So far, we have considered situations in which yp sych a reinforcing stimulus is presented after each response (or, in the case of extinction, not at all). But usually not every response is reinforced. Sometimes a kind word is ignored; sometimes it is appreciated. Not every fishing trip is rewarded with a catch, but some are, and that is enough to keep a person trying. The term intermittent reinforcement refers to situations in which not every occurrence of a response is reinforced. The relation between responding and reinforcement usually follows one of two patterns: each response has a certain probability of being reinforced, or responses are reinforced after particular intervals of time have elapsed. Probability-based patterns require a variable number of responses for each reinforcer. Consider the performance of an archer shooting arrows at a target. Suppose that the archer hits the bull’s-eye one-fifth of the time. On average, he will have to make five responses for every reinforcement (hitting the bull’s-eye); the ratio of responding to reinforcement is five to one. The number of reinforcers the archer receives is directly proportional to the number of responses he makes. If he shoots more arrows (that is, if his rate of responding increases), he will receive more reinforcers, assuming that he does not get tired or careless. Behaviour analysts refer to this pattern of intermittent reinforcement as a ratio schedule of reinforcement. In the laboratory, the apparatus controlling the operant chamber
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Most behaviour is acquired through an organism’s interaction with reinforcing and punishing yp events in its environment. In fact, Skinner develh syc oped a technique, called shaping, to teach new behaviours to his subjects. Shaping involves reinforcing any behaviour that successively approximates the desired response. Imagine that we want to train a rat to press a lever when a red light is lit (the discriminative stimulus) in an operant chamber. Although the rat has used its paws to manipulate many things during its lifetime, it has never before pressed a lever in an operant chamber. And when it is first placed in the chamber, it is not likely to press the lever even once on its own. The lever on the wall of the chamber is attached to an electrical switch that is wired to electronic control equipment or a computer. A mechanical dispenser can automatically drop pellets of food into a dish in the chamber. Thus, the delivery of a food pellet can be made dependent on the rat’s pressing the lever. Before we can shape lever pressing, we must make the rat hungry. We do so by letting the animal eat only once a day. When we know that it is hungry, we place the animal in the operant chamber and then train it to eat the food pellets as they are dispensed from the pellet dispenser. As each pellet is delivered, the dispenser makes a clicking sound. This sound is important. No matter where the rat is in the operant chamber, it can hear the sound, which indicates that the food pellet has been dispensed. Once the rat is hungry and has learned where to obtain food, we are ready to shape the desired response. We make the operation of the pellet dispenser contingent on the rat’s behaviour. We start by giving the rat a food pellet for just facing in the direction of the lever. Next, we wait until the rat makes a move towards the lever. Finally, we give the rat a piece of food only if it touches the lever. Soon, our rat performs like Thorndike’s cats: it makes the same response again and again. Shaping is a formal training procedure, but something like it also occurs in the world outside the laboratory. A teacher praises poorly formed letters produced by a child ee
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who is just beginning to print. As time goes on, only more accurately drawn letters bring approval. The method of successive approximations can also be selfadministered. Consider the acquisition of skills through trial and error. To begin with, you must be able to recognise the target behaviour – the behaviour displayed by a person having the appropriate skill. Your first attempts produce behaviours that vaguely resemble those of a skilled performer, and you are satisfied by the results of these attempts. In other words, the stimuli that are produced by your behaviour serve as reinforcers for that behaviour. As your skill develops, you become less satisfied with crude approximations to the final behaviour; you are satisfied only when your behaviour improves so that it more closely resembles the target behaviour. Your own criteria change as you become more skilled. Skills such as learning to draw a picture, catching a ball, or making a bed are all behaviours that are acquired through shaping. After all, when a child learns these skills, they first learn behaviours that only approximate the final level of skill that they will attain. This process is perfectly analogous to the use of changing criteria in training an animal to perform a complex behaviour.
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machine where you often buy a bar of chocolate. However, if you put money in the machine and do not receive anything in return, your response will extinguish.
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may be programmed to deliver a reinforcer after every fifth response (a ratio of five to one), after every tenth, after every two hundredth, or after any desired number. If the ratio is constant – for example if a reinforcer is programmed to be delivered following every tenth response – the animal will respond rapidly, receive the reinforcer, pause a little while, and then begin responding again. This type of ratio schedule is called a fixed-ratio schedule (specifically, a fixed-ratio 10 schedule). If the ratio is variable, averaging a particular number of responses but varying from trial to trial, the animal will respond at a steady, rapid pace. For example, we might programme a reinforcer to be delivered, on average, after every 50 responses. This type of ratio schedule is called a variable-ratio schedule (specifically, a variableratio 50 schedule). A slot machine is sometimes programmed to deliver money on a variable-ratio schedule of reinforcement. Variable in this instance means that the person cannot predict how many responses will be needed for the next pay-off. The second type of pattern of reinforcement involves time. A response is reinforced, but only after a particular time interval has elapsed. Imagine that you wanted to know what the weather was going to be like because your friends are due to visit, but the weather where they are is quite snowy. In order to keep abreast of the weather, you listen to the half-hourly bulletin on your local radio station. This pattern of intermittent reinforcement is called an interval schedule of reinforcement. After various intervals of time, a response will be reinforced. If the time intervals are fixed, the animal will stop responding after each reinforcement. It learns that responses made immediately after reinforcement are never reinforced. Then it will begin responding a little while before the next reinforcer is available. This type of interval schedule is called a fixed-interval schedule. If the time intervals are variable, an animal will respond at a slow, steady rate. That way, it will not waste energy on useless responses, but it will not miss any opportunities for reinforcement either. This type of interval schedule is called a variable-interval schedule. In a variable-interval 60second schedule of reinforcement, a reinforcer would be delivered immediately following the first response after different time intervals had elapsed. The interval might be 30 seconds at one time, and 90 seconds at another, but, on the average, it will be 60 seconds. An animal whose behaviour is reinforced by this schedule would learn not to pause immediately after a reinforcer was delivered. Instead, it would steadily respond throughout the interval, regardless of the length of the interval. Schedules of reinforcement are important because they show us that different reinforcement contingencies affect the pattern and rate of responding. Think about your own behaviour. How would you perform in subjects in
which your grades were determined by a mid-term and a final exam, or by weekly quizzes, or by unannounced quizzes that occur at variable intervals? What kind of schedule of reinforcement is a salesperson on while waiting on potential customers? Some people work at a slow, steady rate, but others work furiously after long periods of inactivity. Can it be that in the past their work habits were shaped by different schedules of reinforcement?
Resistance to extinction and intermittent reinforcement A response that has been reinforced intermittently is more resistant to extinction. A response that has been continuously reinforced is much less likely to be so resistant. Baldwin and Baldwin (1998) illustrate this by citing the example of two girls who were prone to throwing temper tantrums. Connie (for it is she) received continuous reinforcement for her tantrums by her parents. Whenever she would throw a tantrum, her parents would pay her attention. Paula (for it is she), however, received only intermittent reinforcement – her parents had two other children and would only pay attention to her tantrums about once in every six episodes. This, as you now know, is a typical variable-ratio 6 method of reinforcement. When they joined school, the teacher expressed unhappiness at the tantrums and suggested that the parents undertake a programme of extinction: they were asked to ignore all tantrums. What happened? On the first day of extinction, Connie actually experienced more tantrums (20 per cent more – Lerman and Iwata, 1995) but this dropped to zero in the next few days. Paula’s behaviour, on the other hand, was less resistant to extinction. It took 2–3 weeks for the tantrums gradually to reduce. She continued to throw tantrums long after Connie had stopped. Why? Well, Connie’s behaviour changed because previously continuously reinforced behaviour was now not reinforced at all. Her behaviour received no reinforcement and because her tantrums did not attract the necessary attention, they stopped. They increased on the first day because Connie believed she had to produce more behaviour to receive her reinforcement. When she realised that this behaviour would not be reinforced, she stopped. Paula’s behaviour, however, had previously been intermittently reinforced (every sixth tantrum) and so the new schedule had little effect on her tantrums because she had become accustomed to receiving no reinforcement for her behaviour. On the first day of the programme, therefore, she behaved as she normally would because it was pretty much like normal. Her extinction was gradual and longer than Connie’s because it took a longer period to realise that reinforcement was completely absent rather than intermittent.
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Generalisation and discrimination In classical conditioning, generalisation means that stimuli resembling the CS also elicit the CR. In operant conditioning, generalisation means that stimuli resembling a discriminative stimulus also serve as discriminative stimuli for a particular response. In operant conditioning, as in classical conditioning, generalisation can be reduced through discrimination training. In classical conditioning, discrimination means that CRs occur only in response to certain CSs and not to other, similar stimuli. In operant conditioning, discrimination means that responding occurs only when a particular discriminative stimulus is present – one that was present while responding was reinforced in the past. Responding does not occur when discriminative stimuli associated with extinction or punishment are present. Obviously, recognising certain kinds of similarities between different categories of stimuli is a very important task in our everyday lives. When we encounter a problem to solve – for example, diagnosing a puzzling disease or improving a manufactured product – we attempt to discover elements of the situation that are similar to those we have seen in other situations and try to apply the strategies that have been successful in the past. That is, we try to generalise old solutions to new problems. Discriminative stimuli can exert powerful control over responding because of their association with the consequences of such responding. In or out of the laboratory, we learn to behave appropriately to environmental conditions. For example, we usually talk about different things with different people. We learn that some friends do not care for sports, so we do not talk about this topic with them because we will receive few reinforcers (such as nods or smiles). Instead, we discuss topics that have interested them in the past.
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activit The previous sections considered rather ee simple examples of reinforced behaviours. yp But people and many other animals are able sych to learn very complex behaviours. Consider the behaviour of a young girl learning to print letters. She sits at her school desk, producing long rows of letters. What kinds of reinforcing stimuli maintain her behaviour? Why is she devoting her time to a task that involves so much effort?
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We have studied reinforcement mainly in terms of primary reinforcers and primary punishers. yp sych Primary reinforcers are biologically significant appetitive stimuli, such as food when one is hungry. Primary punishers are biologically significant aversive stimuli, such as those that produce pain. Behaviour can also be reinforced with a wide variety of other stimuli: money, a smile, kind words, a pat on the back, or prizes and awards. These stimuli, called conditioned (or secondary) reinforcers, acquire their reinforcing properties through association with primary reinforcers. Because it can be exchanged for so many different kinds of primary reinforcers in our society, money is the most common conditioned reinforcer among humans. That money is a conditioned reinforcer can be demonstrated by asking
yourself whether you would continue to work if you could no longer exchange money for food, drink, shelter and other items. Similarly, conditioned punishers acquire their punishing effects through association with aversive events. For example, the sight of a flashing light on top of a police car serves as a conditioned punisher to a person who is driving too fast because such a sight precedes an unpleasant set of stimuli: a lecture by a police officer and a ticket for speeding. A stimulus becomes a conditioned reinforcer or punisher by means of classical conditioning. That is, if a neutral stimulus occurs regularly just before an appetitive or aversive stimulus, then the neutral stimulus itself becomes an appetitive or aversive stimulus. The primary reinforcer or punisher serves as the UCS because it produces the UCR – good or bad feelings. After classical conditioning takes place, these good or bad feelings are produced by the CS – the conditioned reinforcer or punisher. Once that happens, the stimulus can reinforce or punish behaviours by itself. Thus, operant conditioning often involves aspects of classical conditioning. Conditioned reinforcement and punishment are very important. They permit an organism’s behaviour to be affected by stimuli that are not biologically important in themselves but that are regularly associated with the onset or termination of biologically important stimuli. Indeed, stimuli can even become conditioned reinforcers or punishers by being associated with other conditioned reinforcers or punishers. The speeding ticket is just such an example. If an organism’s behaviour could be controlled only by primary reinforcers and punishers, its behaviour would not be very flexible. The organism would never learn to perform behaviours that had only long-range benefits. Instead, its behaviour would be controlled on a moment-to-moment basis by a very limited set of stimuli. Conditioned reinforcers and punishers, such as money, grades, smiles and frowns, allow for behaviour to be altered by a wide variety of contingencies.
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The answer is that her behaviour produces stimuli – printed letters – which serve as conditioned reinforcers. In previous class sessions, the teacher demonstrated how to print the letters and praised the girl for printing them herself. The act of printing was reinforced, and the printed letters that this act produces come to serve as conditioned reinforcers. The child prints a letter, sees that it looks close to the way it should, and her efforts are reinforced by the sight of the letter. Doing something correctly or making progress towards that goal can provide an effective reinforcer. This fact is often overlooked by people who take a limited view of the process of reinforcement, thinking that it has to resemble the delivery of a small piece of food to an animal being taught a trick. Some people even say that because reinforcers are rarely delivered to humans immediately after they perform a behaviour, operant conditioning cannot play a major role in human learning. This assertion misses the point that, especially for humans, reinforcers can be very subtle events.
Aversive control of behaviour Your own experience has probably taught you that punishment can be as effective as positive reinforcement in changing behaviour. Aversive control of behaviour is common in our society, from fines given to speeding motorists to the prison sentences given to criminals. Aversive control of behaviour is common for two main reasons. First, it can be highly effective in inducing behaviour change, producing nearly immediate results. A person given a fine for jumping a red light is likely, at least for a short while, to heed the sign’s message. The very effectiveness of punishment as a means of behaviour change can serve as an immediate reinforcer for the person doing the punishing. Secondly, society cannot always control the positive reinforcers that shape and maintain the behaviour of its members. However, it can and does control aversive stimuli that may be used to punish misconduct. For example, suppose that a young person’s peers encourage antisocial behaviours such as theft. Society has no control over reinforcers provided by the peer group, but it can control stimuli to punish the antisocial behaviours, such as fines and imprisonment.
How punishing stimuli work How does a punishing stimulus suppress behaviour? Punishment, like reinforcement, usually involves a discriminative stimulus. A child’s shouting is usually punished in the classroom but not outdoors during a break. A dog chases a
porcupine, gets stuck with quills, and never chases one again. However, it continues to chase the neighbour’s cat. Most aversive stimuli elicit some sort of protective or defensive response, such as cringing, freezing, hiding or running away. The response depends on the species of animal and, of course, on the situation. If you slap your dog for a misdeed, the dog will cower and slink away, looking clearly ‘apologetic’, because you are in a position of dominance. However, if the dog is struck by a stranger, it may very well react by attacking the person. Both types of behaviour are known as species-specific defence reactions (Bolles, 1970).
Escape and avoidance Negative reinforcement teaches organisms to make responses that terminate aversive stimuli. These responses can make a stimulus cease or the organism can simply run away. In either case, psychologists call the behaviour an escape response: the organism endures the effects of the aversive stimulus until its behaviour terminates the stimulus. In some cases, the animal can do more than escape the aversive stimulus; it can learn to do something to prevent it occurring. This type of behaviour is known as an avoidance response. Avoidance responses usually require some warning that the aversive stimulus is about to occur in order for the organism to be able to make the appropriate response soon enough. Imagine that you meet a man at a party who backs you against the wall and engages you in the most boring conversation you have ever had. In addition, his breath is so bad that you are afraid you will pass out. You finally manage to break away from him (an escape response). A few days later, you attend another party. You begin walking towards the buffet table and see the same man (discriminative stimulus) standing nearby. You decide that you will get some food later and turn away to talk with some friends at the other end of the room (an avoidance response). As we saw earlier, phobias can be considered to be conditioned emotional responses – fears that are acquired through classical conditioning. But unlike most classically conditioned responses, phobias are especially resistant to extinction. If we classically condition an eyeblink response in a rabbit and then repeatedly present the CS alone, without the UCS (puff of air), the response will extinguish. However, if a person has a phobia for cockroaches, the phobia will not extinguish easily even if they encounter cockroaches and nothing bad happens. Why does the response persist? Most psychologists believe that the answer lies in a subtle interaction between operant and classical conditioning. The sight of a cockroach makes a person with a
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cockroach phobia feel frightened, that is, they experience an unpleasant conditional emotional response. The person runs out of the room, leaving the cockroach behind and reducing the unpleasant feelings of fear. This reduction in an aversive stimulus reinforces the avoidance response and perpetuates the phobia.
Conditioning of flavour aversions You have probably eaten foods that made you sick and now avoid them on the basis of their flavour alone. The association of a substance’s flavour with illness, which is often caused by eating that substance, leads to conditioned flavour-aversion learning. The study of flavour-aversion learning is important not only because it is a real-life experience, but also because it has taught psychologists about unique relations that may exist between certain CSs and certain UCSs. Just as punishment is a result of classical conditioning where a speciestypical defensive response becomes classically conditioned to a discriminative stimulus, conditioned flavour aversions are acquired in the same way. The flavour is followed by an unconditional stimulus (sickness) that elicits the unpleasant responses of the autonomic nervous system, such as cramping and retching. Then, when the animal encounters the flavour again, the experience triggers unpleasant internal reactions that cause the animal to stop eating the food. Many learning researchers once believed that nearly any CS could be paired with nearly any UCS to produce nearly any CR. However, in a now classic experiment, Garcia and Koelling (1966) showed that animals are more prepared to learn some types of relation among stimuli than others. In the first phase of their experiment, Garcia and Koelling permitted rats to drink saccharine-flavoured water from a tube. Each lick from the tube produced three CSs: taste, noise and bright lights. This phase ensured that rats were equally familiar with each of the CSs. In the next phase, the rats were divided into four groups, each experiencing either ‘bright-noisy’ water or ‘tasty’ water. Each CS was paired with illness or electric shock. After several trials, the experimenters measured the amount of saccharine-flavoured water the rats consumed. They found that the rats learned the association between flavour and illness but not between flavour and pain produced by electric shock. Likewise, the rats learned the association between the ‘bright-noisy’ water and shockinduced pain but not between the ‘bright-noisy’ water and illness. The results make sense; after all, the animal has to taste the flavour that makes it ill, not hear it, and in the world outside the laboratory, a particular flavour does not usually indicate that you are about to receive an electric shock.
This experiment draws two important conclusions: (1) rats can learn about associations between internal sensations (being sick) and novel tastes, and (2) the interval between the two stimuli can be very long. These facts suggest that the brain mechanisms responsible for a conditioned flavour aversion are different from the ones that mediate an aversion caused by stimuli applied to the outside of the body (such as a painful foot shock). It appears that conditioned flavour aversions serve to protect animals from poisonous foods by enabling them to learn to avoid eating them. Because few naturally occurring poisons cause sickness immediately, neural mechanisms that mediate conditioned flavour aversions must be capable of learning the association between events that are separated in time. Most other cause-and-effect relations involve events that occur close in time; hence the neural mechanisms that mediate an organism’s ability to learn about them operate under different time constraints. Some animals have eating habits quite different from those of rats; they eat foods that they cannot taste or smell. For example, some birds eat seeds that are encased in a tasteless husk. They do not have teeth, so they cannot break open the husk and taste the seed. Thus, they cannot use odour or taste as a cue to avoid a poison. However, Wilcoxon et al. (1971) found that quail (a species of seed-eating birds) can form a conditioned aversion to the sight of food that earlier made them sick. People can also acquire conditioned flavour aversions. A friend of mine often took trips on aeroplanes with her parents when she was a child. Unfortunately, she usually got airsick. Just before take-off, her mother would give her some spearmint-flavoured chewing gum to help relieve the pressure on her eardrums that would occur when the plane ascended. She developed a conditioned flavour aversion to spearmint gum. In fact, the odour of the gum still makes her feel nauseated. Conditioned flavour aversions, like most learning situations, involve both classical and operant conditioning. From one point of view, we can say that the aversive stimuli produced by the poison punish the behaviour of eating a particular food. That is, the flavour serves as a discriminative stimulus for a punishment contingency (operant conditioning). However, it also serves as a conditioned stimulus for a classical conditioning situation: the flavour is followed by an unconditional stimulus (the poison) that elicits unpleasant responses of the autonomic nervous system, such as cramping and retching. Then, when the animal encounters the flavour at a later date, it experiences unpleasant reactions that cause it to leave the source of the stimulus and avoid the food.
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Psychology in action – Flavour aversions Because conditioned flavour aversions can occur when particular flavours are followed by feelings of nausea, even several hours later, this phenomenon has several implications for situations outside the laboratory. An unfortunate side effect of chemotherapy or radiation therapy for cancer is nausea. Besides killing the rapidly dividing cells of malignant tumours, both chemotherapy and radiation kill the rapidly dividing cells that line the digestive system and thus cause nausea and vomiting. Knowing what we know about conditioned flavour aversions, we might predict that chemotherapy or radiation therapy would cause a conditioned aversion to the foods a patient ate during the previous meal. Bernstein (1978) showed that this prediction is correct. She gave ice cream to some cancer patients who were about to receive a session of chemotherapy and found that several months later, 75 per cent of these patients refused to eat ice cream of the same flavour. In contrast, control subjects who did not taste it before their chemotherapy said that they liked it very much. Only one trial was necessary to develop the conditioned flavour aversion. Even when patients have a clear understanding that the drugs are responsible for their aversion and that the food is really wholesome, they still cannot bring themselves to eat it (Bernstein, 1991). Thus, a conditioned food aversion is not a result of cognitive processes such as reasoning or expectation. Questionnaires and interviews reveal that cancer patients develop aversions to the foods that they normally eat even if their treatment sessions occur several hours after the previous meal (Bernstein et al., 1982; Mattes et al., 1987). When patients receive many treatment sessions, they are likely to develop aversions to a wide variety of foods. Because a treatment that produces nausea may cause the development of a conditioned flavour aversion to the last thing a person has
Applications of operant conditioning to human behaviour Instructional control activit
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Human behaviour is influenced not only by reinforcement but also by the interactions of yp reinforcement with rules, that is, verbal descripsych tions of the relation between behaviour and reinforcement. In fact, much of our everyday behaviour involves following rules of one sort or another. Cooking from a recipe, following directions to a friend’s house, and obeying the speed limit are common examples. Because ee
eaten, Broberg and Bernstein (1987) attempted to attach the aversion to a flavour other than one that patients encounter in their normal diets. Cancer patients ate either a coconut or root beer Lifesaver (a sweet) after the last meal before a chemotherapy session. The experimenters hypothesised that the unique flavour would serve as a scapegoat, thus preventing a conditioned aversion to patients’ normal foods. The procedure worked; the patients were much less likely to show an aversion to the food eaten during the last meal before the treatment. Conditioned flavour aversions can also have useful applications. For example, psychologists have applied conditioned aversions to wildlife control. In regions where coyotes have been attacking sheep, they have left chunks of dog food laced with an emetic drug wrapped in pieces of fresh sheepskin. The coyotes eat the bait, become sick and develop a conditioned aversion to the smell and taste of sheep (Gustavson and Gustavson, 1985). These methods can help protect endangered species as well as livestock. Mongooses have been introduced into some islands in the Caribbean, where they menace the indigenous population of sea turtles. Nicolaus and Nellis (1987) found that a conditioned aversion to turtle eggs could be established in mongooses by feeding them eggs into which an emetic drug had been injected. Evidence suggests that for some species, conditioned flavour aversions can become cultural traditions. Gustavson and Gustavson (1985) reported that after adult coyotes had developed a conditioned aversion to a particular food, their offspring, too, avoided that food. Apparently, the young coyotes learned from their mothers what food was fit to eat. However, Nicolaus et al. (1982) found that adult racoons having a conditioned aversion to chickens did not teach their offspring to avoid chickens. In fact, after seeing the young racoons kill and eat chickens, the adults overcame their aversion and began preying on chickens again.
rules have the potential to influence our behaviour in almost any situation, behaviour analysts are interested in learning more about how rules and reinforcement interact. One way to investigate this interaction is to give subjects rules that are false, that is, rules that are inaccurate descriptions of the behaviour required for reinforcement (Galizio, 1979; Baron and Galizio, 1983). In such experiments, people may behave in accordance with either the rule or the reinforcement requirement. Other researchers have shown that people sometimes generate their own rules about the consequences of their behaviour (Lowe, 1979). Lowe argues that our ability to describe verbally the consequences of our behaviour explains why humans
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often respond differently from other animals when placed under similar reinforcement contingencies (Lowe et al., 1983). When exposed to fixed interval schedules, animals do not respond immediately after each reinforcement. As time passes, though, responding gradually increases until the next reinforcer is delivered. Humans, on the other hand, tend to follow one of two strategies: responding very slowly or responding very rapidly. Those people who respond slowly often describe the schedule as intervalbased and they respond accordingly. Those who respond rapidly usually describe the schedule as ratio-based – which it is not – and they respond accordingly. Thus, the language one uses may indeed exert some control over one’s own behaviour. The extent to which language and other behaviours interact is the subject of ongoing experimental and theoretical work (Hayes, 1989; Cerruti, 1990).
Stimulus equivalence Stimulus equivalence refers to the emergence of novel behaviour without direct reinforcement of that behaviour (Fields, 1993; Fields et al., 1995). Imagine that you were asked to learn the relationship among a group of symbols: A, B and C. Suppose further that after training without reinforcement, you discovered that A = B and A = C. How then would you respond to the following question: does B = C? You would probably reason that if A = B and A = C, then B, too, is equal to C. But notice that you were never trained or received any direct reinforcement for learning that B = C. Rather, the equivalent relationship between B and C emerged from your previous learning; hence, the term ‘stimulus equivalence’. Stimulus equivalence is an important area of research because it represents one way we learn to use and understand symbols, such as language. For example, let A
represent a picture of a dog, B represent the spoken word ‘dog’, and C represent the printed word ‘dog’. Suppose that we teach a child to point to the picture of the dog (A) and say the word ‘dog’ (B). In this case, the child learns that A = B and B = A. Next, suppose that we teach the child to point to the picture of the dog (A) when he sees the printed word ‘dog’ (C). The child learns that A = C and that C = A. What we are really interested in, though, is whether the child will have learned that the spoken word ‘dog’ (B) is equivalent to, or means the same thing as, the printed word ‘dog’ (C). This is precisely what children learn under these circumstances, even though the equivalent relationship, B = C, has not been directly trained (Sidman and Tailby, 1982). Rather, it emerged as a consequence of the child’s learning history. Understanding how stimulus equivalence develops is likely to lead to a better understanding of language development.
Drug use and abuse Soon after Skinner outlined the principles of operant behaviour, others were quick to apply them to the study of drug action and drug-taking (Thompson and Schuster, 1968). In fact, Skinner’s three-term contingency is now partly the basis of an entirely separate discipline of pharmacology known as behavioural pharmacology, the study of how drugs influence behaviour. In this field, the terms ‘discriminative stimuli’, ‘responding’ and ‘consequences’ translate into drugs as discriminative stimuli, the direct effects of drugs on behaviour, and the reinforcing effects of drugs, respectively. Perhaps the most interesting discovery in behavioural pharmacology is the finding that most psychoactive drugs function as reinforcers in both humans and animals.
Controversies in Psychological Science – What is insight? The issue
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Many problems we have to solve in our daily lives require us to make responses that we have never made before and that we activit have never seen anyone else make either. We often think ee about a problem, looking at the elements and trying to yp sych imagine various solutions. We try various responses in our heads, but none seems to work. Suddenly, we think of a new approach: maybe this one will work. We try it, and it does. We say that we have solved the problem through insight (Sternberg and Davidson, 1996). But what is insight? Some people see it as almost a magical process: a sudden flash of inspiration, a bolt from the blue. At
the simplest level, it is a form of understanding that changes a person’s perception of a problem and its solution (Dominowski and Dallob, 1996). Most people regard insight as a particularly human ability – or, at least, as an ability that belongs to our species and, perhaps, some of the higher primates. Some psychologists, however, regard the term as fairly meaningless.
The evidence During the early part of the twentieth century, the German psychologist Wolfgang Köhler studied the problem-solving behaviours of chimpanzees. In one famous example (Köhler, 1927), he hung some bananas from the ceiling of an animal’s
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Controversies in Psychological Science – Continued cage, just high enough to be out of reach. The cage also contained a large box. Sultan, one of the chimps, first tried to jump up to reach the bananas, then paced around the cage, stopped in front of the box, pushed it towards the bananas, climbed onto the box, retrieved and ate the fruit. Later, when the bananas were suspended even higher, he stacked up several boxes, and on one occasion when no boxes were present, he grabbed Köhler by the hand, led him over to the bananas and climbed on top of him. Figure 7.10 illustrates the attempts at solving the problem. Köhler believed that the insightful problem-solving behaviour shown by the chimpanzees was different from the behaviour of Thorndike’s cats as they learned to escape the puzzle boxes. The cats clearly showed trial-and-error behaviour, coming upon the solution by accident. The escape from the box served as a reinforcing stimulus, and eventually the animals learned to operate the latch efficiently. But the behaviour of the chimpanzees seemed very different. They suddenly came upon a solution, often after looking at the situation (and, presumably, thinking about it). Köhler saw no accidental trial-and-error behaviour. The problem used in Köhler’s experiment is an example of an object-use problem. Another type of problem, a spatial insight problem (Dominowski and Dallob, 1996) is seen in Figure 7.11. This is the nine dot problem in which you have to connect all the dots using four straight lines and without lifting your pen from the page or retracing any of the lines. Research suggests that insight may be less mysterious than it appears and may be based on combinations of behaviours initially learned through trial and error. In one study (Epstein et
Figure 7.11 The nine dot problem. The challenge is to connect all nine dots using four straight lines without retracing any lines and without lifting your pen. The solution is seen in the figure on the right. Source: Dominowski, R.L. and Dallob, P. Insight and problem solving. In Sternberg, R. and Davidson, J. (eds), The Nature of Insight. Cambridge, MA: MIT Press, 1996. Reproduced with permission from MIT Press.
al., 1984), the experimenters used operant procedures (with food as the reinforcer) to teach a pigeon two behaviours: (1) to push a box towards a target (a green spot placed at various locations on the floor), and (2) to climb onto a box and peck at a miniature model of a banana which was suspended overhead. Once these behaviours had been learned, the experimenters confronted the pigeon with a situation in which the box was in one part of the chamber and the banana was in another. The pigeon acted much the way that Sultan did: At first, the bird appeared to be confused: it stretched toward the banana, turned back and forth from the banana to the box, and so on. Then, rather suddenly, it began to push the box toward th